Harper won the 2010 Golden Spikes Award, awarded annually to the best amateur baseball player. Going into the 2012 season, baseball prospect-watchers, including Baseball America, MLB.com, and Baseball Prospectus routinely ranked Harper as a top-3 prospect. He made his MLB debut with the Nationals on April 28, 2012. Harper was selected for the 2012 All-Star Game, becoming the youngest position player to ever be selected. He has been touted as a "five-tool player".
Harper won the NL Rookie of the Year Award in 2012. He tied for the NL lead in home runs in the 2015 Major League Baseball season, and was named the National League Most Valuable Player for 2015 by unanimous decision of the Baseball Writers' Association of America.
Harper attended Las Vegas High School. After his sophomore year, he earned his General Educational Development (GED) in October 2009, making him eligible for the June 2010 amateur draft in order to begin his professional baseball career earlier.
For the 2010 college season, 17-year-old Harper enrolled at the College of Southern Nevada of the Scenic West Athletic Conference (SWAC) in the National Junior College Athletic Association (NJCAA), where he would play catcher. His older brother Bryan, who had been his teammate at Las Vegas High School, was one of the Southern Nevada Coyotes' starting pitchers, and the brothers often worked as a battery. An advantage for Harper in his eventual transition to his professional career was that the SWAC, like MLB, uses wooden bats in conference play. In 66 games, he hit 31 home runs, 98 RBIs, hitting .443/.526/.987 (AVG/OBP/SLG). His 31 home runs shattered the school's previous record of 12. He was named the 2010 SWAC Player of the Year.
In the Western district finals of the 2010 NJCAA World Series, Harper went 6-for-7 with 5 RBIs and hit for the cycle. The next day, in a doubleheader, he went 2-for-5 with a three-run double in the first game, and in the second game went 6-for-6 with 4 home runs, a triple, and a double.
On June 2, 2010, Harper was ejected from a National Junior College World Series game by home plate umpire Don Gilmore after a called third strike. Harper drew a line in the dirt with his bat as he left the plate, presumably to show where he thought the pitch was. It was Harper's second ejection of the year, and resulted in a two-game suspension. The suspension ended his amateur career, as Southern Nevada lost the game from which Harper was ejected and lost their next game with Harper suspended, which eliminated them from the tournament. Harper won the 2010 Golden Spikes Award.
Harper was drafted No. 1 overall by the Washington Nationals in the 2010 MLB Draft, making Harper the second consecutive number one overall pick of the Major League Baseball Draft taken by the Nationals. The Nationals took Stephen Strasburg in 2009. Although Harper had previously and predominantly played catcher, the Nationals drafted him as an outfielder to extend his career and to accelerate his player development, so that he could debut in MLB earlier.
Harper was represented by Scott Boras. Following in Strasburg's footsteps, Harper held out until the very last minute before the deadline. With twenty-six seconds remaining, Harper and the Nationals agreed to a 5-year contract worth $9.9 million, including a $6.25 million signing bonus, and eight semesters of college tuition. When asked about the signing, Nationals President Stan Kasten said, "The truth is, with a full minute to go, Mike and I both thought we were not going to have a deal." Asked what changed in that final minute, Nationals General Manager Mike Rizzo replied, "It was both sides compromising and knowing that we were so close, it would be fruitless not to get a deal done." On August 26, 2010, Harper was introduced by the Nationals. Harper said he chose to wear No. 34 because "I always loved Mickey Mantle, three and four equals seven."
After batting .319 with a .407 OBP (and leading his team in hits, homers, RBIs, and walks) in the Nationals' fall instructional league, Harper was selected to participate in the Arizona Fall League as a member of the Scottsdale Scorpions taxi-squad, the second-youngest player in the history of the league (two days older than when Mets' prospect Fernando Martínez appeared in the league in 2006). He batted .343 and slugged .729. On November 20, Harper and the Scottsdale Scorpions won the 2010 Arizona Fall League Championship.
After batting .399 in spring training, the Nationals optioned Harper to the Hagerstown Suns of the Class-A South Atlantic League to begin his minor league career. In April 2011, after a slow start in the minor leagues, Harper visited optometrist Dr. Keith Smithson, who reportedly told him, "I don't know how you ever hit before. You have some of the worst eyes I've ever seen." In his first 20 games after receiving contact lenses, Harper hit .480, collecting 7 home runs, 10 doubles and 23 RBIs.
Harper was selected to represent the United States in the 2011 All-Star Futures Game during the 2011 All Star Game weekend. He was promoted to the Double-A Harrisburg Senators on July 4. Harper went 2 for 3 in his AA debut with two singles, a run, and a walk.
On August 18, 2011, Harper injured his hamstring while running from first to third base on an extra base hit. The injury was severe enough that he had to be carried off the field by his coaches. Harper was placed on the 7-day disabled list, and it was reported that the injury had ended Harper's season.
During 2012 spring training, Harper was optioned to Triple-A Syracuse, where he started the season, playing exclusively at the center field position. Harper was called up to the Nationals on April 27, 2012 after Ryan Zimmerman was placed on the DL. He made his MLB debut with the Nationals the next day against the Los Angeles Dodgers. Harper grounded out to the pitcher (Chad Billingsley) in his first Major League at bat. He recorded his first Major League hit with a double in his third at-bat against Billingsley and got his first RBI on a sacrifice fly in the top of the ninth against Javy Guerra.
After being hit by a pitch by Cole Hamels in the first inning of a game against the Phillies on May 6, 2012, Harper eventually advanced to third, then stole home plate, becoming the first teenager to steal home plate since 1964. Hamels later admitted to hitting Harper intentionally, and was suspended five games by MLB. On May 14, 2012, Harper hit his first Major League home run off of San Diego Padres pitcher Tim Stauffer. He was the youngest player to homer in the major leagues since Adrián Beltré did in 1998. He was named National League Rookie of the Month for May.
Harper earned his first walkoff hit on June 5, 2012, with an RBI single in the bottom of the 12th inning against the New York Mets.
During a game against the Toronto Blue Jays on June 12, 2012, Harper hit a deep home run to center field that struck an advertising banner adjacent to the restaurant in the second tier of seats at the Rogers Centre, estimated to travel 438 feet. After the game, a reporter asked if Harper would take advantage of Ontario's lower drinking age (19, versus 21 in the U.S.) by drinking a celebratory beer with his teammates. Harper replied, "I'm not going to answer that. That's a clown question, bro." The comment quickly developed into an Internet meme, and the phrase itself repeated, in response to a question, by Senate Majority Leader Harry Reid. Harper filed an application to trademark the phrase.
Harper was named a candidate in the All-Star Final Vote, with the winner being added to the All-Star Game roster. Harper finished third behind David Freese and Michael Bourn. However, Bourn would make the roster after Ian Desmond sustained an injury and Harper would become the youngest position player (and third-youngest player, behind Dwight Gooden and Bob Feller) to ever make an All-Star roster when it was announced Giancarlo Stanton would undergo knee surgery. "I don't have words to explain it right now. It's exciting to go. I'm excited to get there and be around all the top guys in the country, of course, and the top guys in baseball. I'm going to take it all in and try to enjoy it with my family and just be as mellow and as calm as I can be", Harper stated. He went 0-for-1 with a strikeout and a walk.
Harper struggled in the games following the All-Star break, hitting .176 with 26 strikeouts in his first 116 plate appearances in the second half. Manager Davey Johnson began to give Harper days off due to his poor play and visible on-field frustration. Johnson said that Harper had become "overly aggressive" at the plate.
Harper's play began to improve in late August. He hit two home runs in a game against the Miami Marlins on August 29, 2012, his first career multi-homer game, and recorded his first major league ejection after throwing his helmet down in the ninth inning in response to hitting into a double play. He had a second multi-homer game on September 5, 2012, against the Chicago Cubs. Harper was named Rookie of the Month again in September after hitting .330 with seven home runs. Harper's 254 total bases and 57 extra base hits were the most ever for a player under age 20, while his 22 home runs, 98 runs scored, .340 on-base percentage, .477 slugging percentage, and .817 on base-plus-slugging were the best regular season totals for a teenager in the past 45 years.
In Game 5 of the 2012 NLDS against the St. Louis Cardinals, Harper hit his first postseason home run. The Nationals would eventually lose the game 7–9 despite leading by 6 runs. He finished his first postseason appearance with a .130 batting average.
Harper was named the National League Rookie of the Year. He received 112 votes, 16 of them first-place votes, beating Arizona's Wade Miley (105 votes, 12 first-place) and Cincinnati's Todd Frazier.
Harper hit two home runs on Opening Day of the 2013 season against the Miami Marlins. He became the youngest major league player, at age 20, to hit two home runs in his team's first game of the season. He was voted a starter for the MLB All Star Game, his second career All-Star selection.
After hitting 13 home runs in just 58 games, Harper was selected to participate in the 2013 Home Run Derby. Harper hit a total of 16 home runs in the first two rounds to advance to the final round, in which he faced Yoenis Céspedes, an outfielder for the Oakland Athletics. Although he lost 9–8 in the finals, Harper was the second-youngest player to participate in the Home Run Derby, and the youngest to ever make it to the final round. Harper hit his 17th homer of the season on August 6 and it was his 39th of his career, passing Ken Griffey Jr. for most home runs by a player younger than 21. Only 2 other players have more home runs than him before turning 21. In 118 games, he hit .274/.368/.486 with 20 HR, 58 RBI and 47 XBH. During the 2013 off-season, Harper successfully underwent left knee surgery to remove a bursa sac.
During a game against the San Diego Padres on April 25, 2014, Harper suffered a left thumb injury when sliding to 3rd base on a 3-run triple. He was placed on the 15-day disabled list the next day on April 26. An MRI revealed that the thumb had a torn ulnar collateral ligament. On April 28, 2014, it was announced that Harper would require surgery to repair the ligament tear in the thumb. During a rehab game with the Double-A Harrisburg Senators on June 28, 2014, Harper hit 3 home runs in a single game. Harper returned to the Majors on June 30, 2014. In 100 games of 2014, Harper batted .273 with 13 home runs and 32 RBI.
After the 2014 season, Harper would travel to Japan to participate in the 2014 Major League Baseball Japan All-Star Series, but later withdrew.
On April 18, 2015, Harper hit the longest home run of his professional career with a 461-foot home run to center field against the Philadelphia Phillies. On May 6, Harper hit three home runs in a single game for the first time in his career against Tom Koehler with one of the shots going 442 feet to the second deck in a 7–5 victory over the Miami Marlins, becoming the youngest player to accomplish this feat since Joe Lahoud in 1969. Harper was later awarded the Player of the Month Award for the month of May for the first time in his career.
Measured by adjusted OPS (OPS+) Harper's 2015 was a top 5 hitting season (since 1900) for all players under the age of 23, and the best season of any hitter since Barry Bonds a decade earlier. He also led the majors in WAR and tied for the NL home run title with 42. Harper also became the youngest player ever with at least 40 home runs and 120 walks in one season, a distinction previously held by Babe Ruth.
Baseball America named Bryce the 2015 player of the year. On October 31, Harper was named the National League winner of the 2015 Hank Aaron Award. On November 19, Harper was selected as the 2015 National League Most Valuable Player by unanimous decision. With his MVP win, Harper became the youngest player to unanimously win the MVP at age 23. Harper also became the first player in Nationals/Expos history to win an MVP award, and the first player that played for a Washington team to win one. ESPN chose him as their 2015 MLB Person of the Year.
On April 14, 2016, Harper hit his first career grand slam for his 100th career home run in a game against the Atlanta Braves. Three days later, he hit a home run for a fourth straight game, setting a new career streak for most consecutive games with a home run. He was named National League Player of the Week on April 18, after driving in 12 runs, tying a club record for home runs in consecutive games and becoming the eighth-youngest player in major league history to reach 100 home runs.
On May 8, 2016, Harper was walked six times in a game against the Chicago Cubs, tying the MLB record for most walks in a game. Harper also reached base seven times (besides the six walks he was also hit by a pitch), becoming the first player in over 100 years to reach base seven times without recording an at bat. In total, Harper was walked 13 times in the four-game series, setting a new MLB record for most walks in a series. On May 9, 2016, Harper was ejected for yelling at Brian Knight from the dugout when Danny Espinosa was called out on strikes. Harper returned to the field to celebrate the win with his teammates and was caught shouting profanity towards Knight. Two days later, Harper was given a one-game suspension and an undisclosed fine, but Harper appealed the same day. On May 14, Harper dropped his appeal, and began serving the one-game suspension. In 147 games of 2016, Harper finished with a .243 batting average, 24 home runs, and 86 RBI. He also walked 108 times, and 20 of them were intentional that led MLB.
The Nationals finished the season with a 95-67 record, clinching the NL East division, but lost to the Dodgers in the 2016 NLDS.
On April 3, 2017, Harper hit a solo home run, struck out, and was walked on Opening Day against the Miami Marlins. Harper's home run was his fifth career opening day home run, the most by a player younger than 25. He set the MLB record for runs scored in the month of April with 32 against the New York Mets, surpassing Larry Walker's 29 in 1997.
On May 13, Harper and the Nationals avoided arbitration in 2018 by agreeing to a one-year, $21.625-million contract. That night, he hit a walk-off home run vs. the Philadelphia Phillies for the second time in the 2017 season, after doing it on April 16 as well.
On May 16, 2017, Harper hit a home run at PNC Park, which meant in his career he had hit a home run in all 15 National League ballparks.
On May 29, in a game against the San Francisco Giants, Harper was hit by a pitch from Hunter Strickland. Harper had hit two home runs off of Strickland in the 2014 National League Division Series (a series the Giants won), leading Harper to believe Strickland was seeking revenge. Harper slammed down his bat and charged the mound, throwing his helmet wide of Strickland before the two players exchanged punches, starting a bench-clearing brawl in which Giants first baseman Michael Morse, one of several former Nationals teammates of Harper on the Giants team, suffered a serious concussion in a collision with Giants pitcher Jeff Samardzija. Both Harper and Strickland were ejected for their role in the brawl. The next day, on May 30, Harper was suspended four games. Harper appealed, and his suspension was reduced to three games. Harper credited Morse with preventing him from injury during the scrum, as Morse had absorbed a body blow from Samardzija that appeared to be aimed at Harper, telling a MASN reporter, "I'm very thankful for Mikey Mo."
Harper was the top overall vote-getter for the National League to start in the 2017 Major League Baseball All-Star Game and received the most votes of any one player overall. The starting right fielder for the National League All-Stars, he went 1-for-1 with a walk and made a diving catch on defense to rob American League catcher Salvador Pérez of a base hit. He wore cleats honoring the late Miami Marlins ace José Fernández, a division rival pitcher who had held Harper to a .211 batting average against for his career before his September 2016 death in a boat crash, for the All-Star Game.
On July 27, Harper hit one of four consecutive home runs by Nationals hitters off Milwaukee Brewers starter Michael Blazek, the first time the feat had been accomplished in Major League Baseball since the 2011 season. On August 7, he hit his 150th home run. He was 24 years and 295 days old when he accomplished this feat, exactly the same age as Los Angeles Angels superstar Mike Trout when he hit his 150th home run. On August 12, Harper suffered a hyperextended left knee after reaching first base and left the game. It was later revealed that his left knee had a significant bone bruise, but no ligament damage, sending him to the disabled list but prompting team officials to say they were confident he could return before the end of the season.
Harper has been known to stay in the dugout until the final out of All-Star Games, even though in that particular game, an exception permits that once the manager removes the starters from play they are not obligated to remain. Many promptly shower then leave the park. During each of his first four All-Star Games, Harper indicated that he had remained for the entire game, anticipating the opportunity to re-enter should his team require it due to a shortage of players by reason of either injury or ejection.
Harper is known for hitting home runs on Opening Day, and became the first player in MLB history to hit five before the age of 25.
Harper resides in Henderson, Nevada. Harper's father, Ron, is an ironworker in Las Vegas. Harper attributes his work ethic to the lessons he learned from watching his father: "I wanted to come out and I wanted to work hard because he worked hard. He did it for over 25 years."
Harper's older brother, Bryan Harper, is also in the Washington Nationals organization as a pitcher for the Class-AAA Syracuse Chiefs. Bryan was originally drafted in the 31st round out of Las Vegas High School by the Nationals in 2008, but he chose not to sign and played with Bryce for the College of Southern Nevada the following year. He eventually signed with the Nationals after being selected in the 2011 draft in the 30th round, the year after Bryce Harper was drafted first overall by the Nationals. While Bryan Harper has yet to debut in the major leagues, he impressed in his 2016 season and was considered a possible candidate for a promotion before an arm injury that led to him undergoing Tommy John surgery in the off-season. Even while playing on different teams within the Nationals organization, the Harper brothers speak by phone "almost every day" during the baseball season, according to Bryce.
Harper is a member of The Church of Jesus Christ of Latter-day Saints. He has spoken publicly about his decision to abstain from alcohol, although he said in 2014 that he sometimes drinks coffee during the baseball season.
Harper married longtime girlfriend Kayla Varner in a ceremony at the San Diego California Temple in December 2016. The couple were previously engaged in 2014, but their wedding set for January 2015 did not take place. In July 2016, Kayla announced the couple's reconciliation and re-engagement.
Harper owns a customized Mercedes-Benz CLS, outfitted with a low-light glow bat enclosure in the trunk and Nationals curly "W" insignia on the rear of the car replacing the Mercedes logo.
Harper was featured in an episode of ESPN E:60 and was on the cover of Sports Illustrated in May 2009. Harper featured in another ESPN magazine in 2015, this time displaying naked in ESPN's The Magazine 2015 Body Issue. Harper also received a sponsorship deal with a nutritional supplement company focusing on active lifestyles, MusclePharm.