The Orioles selected Arrieta in the 2007 MLB draft, and he debuted for the Orioles in 2010. The Orioles traded Arrieta to the Cubs in 2013. In 2015, Arrieta won the Cy Young Award, was the MLB wins leader, pitched a no-hitter, and set a major league record at 0.75 earned run average (ERA) for the lowest second-half ERA. Arrieta threw his second no-hitter in 2016.
Born in Farmington, Missouri, Arrieta grew up in Plano, Texas, and attended Plano East Senior High School. As a high school senior he was selected by the Cincinnati Reds in the 31st round of the 2004 draft, but instead he chose to attend college.
He attended Weatherford Junior College for his freshman year posting a 6–2 win-loss record with a 3.58 earned run average (ERA). Following his freshman year, Arrieta was selected by the Milwaukee Brewers in the 26th round of the 2005 Major League Baseball draft but instead opted to transfer to Texas Christian University where he played for the Horned Frogs baseball team for his sophomore and junior seasons and studied sport psychology. During the summer of 2005, prior to enrolling at TCU, Arrieta participated in summer collegiate baseball with the McKinney Marshalls of the Texas Collegiate League and posted a 4–3 record in 10 starts with a 1.87 ERA over 62.2 innings pitched. During his sophomore year, Arrieta led college baseball with 14 wins and had a 2.35 ERA over 19 appearances. He also won the Mountain West Conference Pitcher of the Year award and was named a Second-Team College Baseball All-American after his sophomore year.
Arrieta first joined the United States national baseball team in 2006 and helped the team win the World University Baseball Championship in Cuba. He was 4–0 with 34 strikeouts and a 0.27 ERA—allowing just one earned run in 35 innings pitched over six starts for the team. In his first start at the 2008 Summer Olympics, Arrieta pitched six innings and struck out seven in Team USA's 9–1 victory over the China national baseball team.
Arrieta was selected by the Baltimore Orioles in the fifth round of the 2007 Major League Baseball draft and received a $1.1 million signing bonus, which at the time was the largest signing bonus for a fifth round draft pick.
Arrieta made his professional debut in the Arizona Fall League with the Phoenix Desert Dogs in 2007. He posted 16 scoreless innings, while striking out 16 over 14 appearances, and helped lead the Desert Dogs to the Arizona League championship.
Arrieta was 6–5 with a 2.87 earned run average and 120 strikeouts over 113 innings for the Frederick Keys of the Class A-Advanced Carolina League when his season ended in order to allow him to play for the USA Baseball team at the 2008 Summer Olympics in Beijing.
Arrieta made his major league debut on June 10, 2010, against the New York Yankees at Camden Yards. He pitched six innings, giving up four hits and three runs, striking out six and earning the win. He started the home openers for the Orioles in 2011 and 2012. Both starts resulted in victories for the Orioles. After starting the 2012 season 3–9 with an ERA of 6.13, Arrieta was demoted to Triple-A on July 6, 2012. Arrieta began the 2013 season with four starts for the Orioles posting a 1–1 record and a 6.63 ERA until being sent down to the Triple-A Norfolk Tides on April 22, 2013 after the Orioles recalled Alex Burnett. He was recalled by the Orioles on May 18, and then later optioned back down to Triple-A to make room for Kevin Gausman on May 23. He was recalled again on June 14 and Gausman was optioned to Triple-A to make room on the roster for Arrieta. Through four years with the Orioles, Arrieta posted a record of 20–25 and a 5.46 ERA.
On July 2, 2013, the Orioles traded Arrieta along with Pedro Strop to the Chicago Cubs for Scott Feldman and Steve Clevenger. He was optioned to the Iowa Cubs of the Class AAA Pacific Coast League upon being acquired. After making 5 starts for Iowa, Arrieta was recalled to start Game 2 of a doubleheader against the Brewers on July 30. In his Chicago debut, he gave up 1 run in 6 innings, earning a no-decision in the 3–2 loss. After the game, Arrieta was optioned to Iowa where he made 2 more starts before being recalled on August 14 to replace Carlos Villanueva in the rotation. He made eight more starts before the end of the season. In his nine starts with Chicago, he went 4–2 with a 3.66 ERA, striking out 37 in 51.2 innings. In 30 games (29 starts) in 2013 including the minors, Arrieta went 12–9 with a 4.42 ERA, striking out 137 in 154.2 innings.
Arrieta took no-hitters into the seventh or eighth innings three times in the 2014 season. On June 24, Arrieta retired the first 18 Reds in order, but the perfect game was broken up by Cincinnati's Billy Hamilton's leadoff double in the seventh. On June 30, 2014, against the Red Sox, Arrieta took a no-hitter into the 8th until Stephen Drew singled to lead off the inning. As of September 24, 2014, he had posted a 10–5 record with a 2.53 ERA. In 156.2 innings he gave up 114 hits, walked 41, and struck out 167.
On July 12, 2015, Arrieta pitched a complete game victory over the Chicago White Sox at Wrigley Field, his second complete game of the season and the third of his major league career. On August 20, Arrieta became the first MLB pitcher to win 15 games in the 2015 season. Ten days later, Arrieta no-hit the Los Angeles Dodgers at Dodger Stadium for the 14th no-hitter in Cubs history. He struck out 12 batters, including all three batters he faced in both the first and ninth innings. Sandy Koufax had been the last pitcher to complete a no-hitter by striking out all three batters he faced in the ninth inning, doing so against the Cubs in his 1965 perfect game—a game also played at Dodger Stadium. Arrieta was named the NL Player of the Week for August 24–30 and NL Pitcher of the Month for August with a 6−0 and a 0.43 ERA and the no-hitter. The right-hander held opposing hitters to a .130 batting average and a .196 on-base percentage in August and struck out 43 batters while walking just 10. On September 22, Arrieta won his 20th game of the season, throwing a three-hitter against the Brewers. With 11 more strikeouts in that 4-0 Cubs victory at Wrigley, he was the first MLB pitcher to win 20 games this season and had his 4th complete game and 3rd shutout of the season.
After the 2015 All-Star break, he gave up 9 earned runs during 15 starts over 107 1/3 innings for a 0.75 ERA, the lowest in MLB history in the second half. For the season, Arrieta's 22–6 record and 1.77 ERA made him only the fifth pitcher to win at least 22 games with no more than six losses and a sub-2.00 ERA since the earned run became an official stat in 1913. On October 5, he was again named NL Pitcher of the Month for his 4–0 September record with a 0.45 ERA. Arrieta's 2015 season has been widely compared to Bob Gibson's 1968 season in which Gibson won the National League MVP and Cy Young Awards after posting a live-ball era record 1.12 ERA.
Arrieta started the 2015 National League Wild Card Game, He pitched a complete-game shutout, striking out eleven batters and allowed only four hits to defeat the Pittsburgh Pirates 4–0. He became the first pitcher to post a postseason shutout while striking out at least 10 batters and walking zero. He is also the first pitcher to have more stolen bases than runs scored in a postseason game when he stole second base in the top of the 7th. Arrieta was the pitcher of record in the Game 2 loss of the 2015 National League Championship Series to the New York Mets.
On November 18, 2015, Arrieta won the NL Cy Young Award to become the first Cubs pitcher to do so since Greg Maddux in 1992. He is the fifth Cubs winner overall, also joining Fergie Jenkins (1971), Bruce Sutter (1979) and Rick Sutcliffe (1984).
On February 5, 2016, Arrieta and the Cubs agreed on a record arbitration deal worth $10.7 million 2016 salary, the largest one-year contract for a second-time arbitration eligible pitcher, topping David Price's $10.1 million salary in 2013. The club chose him as the 2016 season Opening Day starting pitcher against the Angels on April 4, 2016.
On April 21, 2016, Arrieta pitched his second career no-hitter and the 15th no-hitter in Cubs history against the Cincinnati Reds in a 16–0 blowout win. He walked four and struck out six. Arrieta, who at the time of the no-hitter had not recorded a loss in his last 17 regular-season starts, became only the second MLB pitcher ever to go unbeaten (in regular-season play) between no-hitters, with the only other being Johnny Vander Meer, who threw consecutive no-hitters in 1938. The Arizona Diamondbacks defeated Arrieta and the Cubs 3–2 on June 5, even with 12 strikeouts in his first five innings, stopping a 20-game regular season winning streak and giving him his first loss in 11 months.
In Game 3 of the 2016 NLDS, Arrieta hit a three run home run off of San Francisco Giants' pitcher Madison Bumgarner, the first time that a pitcher hit a home run off of Bumgarner, which ended Bumgarner's consecutive playoff scoreless innings streak, of over 24 innings. Arrieta won Game 2 and Game 6 of the 2016 World Series. The Cubs won Game 7 of the series 8-7 in 10 innings, giving them their first World Series title after a 108-year long drought. On January 13 he agreed to a contract for the 2017 baseball season.
Arrieta throws five different pitches. He throws a four-seam fastball, two-seam fastball, slider/cutter, curveball, and a changeup. His fastball averages around 93-94 mph, sometimes reaching upper-90s mph. He relies on ground balls and swinging strikes. His slider averages 88 miles per hour (142 km/h) with late break peaking out at 92 miles per hour (148 km/h) and his curve sits at 80 miles per hour (130 km/h) with two-plane break. His changeup has tailing motion like a two-seam fastball and ranges from 86 to 89 miles per hour (138 to 143 km/h). Arrieta's great ability to generate movement on his pitches, as well as his unique mechanics make him nearly unhittable when his command is on.
Arrieta lives in Austin, Texas, during the offseason with his wife, Brittany, and their two children, Cooper and Palmer. He is known as a "workout freak" and uses cross-training in his workouts. Arrieta does pilates and incorporates kale juice, nuts, and fruits into his diet. His maternal grandfather is of Puerto Rican ancestry whose parents are from the Basque Country, while his paternal grandmother is of Italian ancestry. Arrieta served as a groomsman for former TCU teammate Matt Carpenter's wedding on December 10, 2011.