Steven Matz was born on May 29, 1991 in Stony Brook, New York, the second child of Ron and Lori Matz. He has an older brother, Jonathan, and younger sister, Jillian. Ron Matz coached a travel baseball team and is a service manager at a Jeep dealership in West Islip. Lori is an administrative employee at Comsewogue High School in Port Jefferson Station, New York. Matz and his family, as far back as his grandparents, are devout fans of the New York Mets. Matz was raised as a non-practicing Lutheran though he joined the evangelical Calvary Chapel while a minor leaguer.
Matz began receiving pitching lessons at age 10, from former MLB pitcher Neal Heaton. He attended Ward Melville High School in East Setauket, New York, and pitched and played first base for the school's baseball team. In high school, he enjoyed a rivalry with nearby Patchogue-Medford High School pitcher, friend and current major leaguer Marcus Stroman (Stroman also took pitching lessons from Neal Heaton for several years). Matz and Stroman were teammates on the same elite travel team, The Paveco Storm, for several years in junior high and high school. The two were roommates during the Area Code Games and pitched against each other multiple times in high school. Despite not receiving attention from college or professional scouts until June of his junior year, Matz was named Newsday's Long Island Player of the Year and was given the Yastrzemski Award as the best high school ballplayer in Suffolk County in his senior year.
The New York Mets selected Matz in the second round, with the 72nd overall selection, of the 2009 Major League Baseball Draft. The Mets did not have a first round pick in that year's draft and did not expect Matz to drop to them in the second round. Some Mets scouts attribute this to his playing high school baseball in the Northeast, an area which does not traditionally produce much high round talent. Matz originally committed to attend Coastal Carolina University to play college baseball for the Coastal Carolina Chanticleers, but the Mets agreed with him on a $895,000 signing bonus ten minutes before the August 15 signing deadline for draft picks. Matz had scheduled a flight to attend his orientation at Coastal Carolina for the next day.
While pitching in an instructional league in 2010, he experienced elbow discomfort. A doctor diagnosed Matz with a torn ulnar collateral ligament of the elbow, requiring Tommy John surgery. He did not make his professional debut until 2012, when he pitched for the Kingsport Mets of the Rookie-level Appalachian League. He compiled a 2–1 win–loss record a 1.55 earned run average (ERA) in 29 innings pitched with Kingsport.
Before the 2013 season, Matz worked on developing a curveball to replace his slider, at the advice of Frank Viola and Ron Romanick. That year, he pitched for the Savannah Sand Gnats of the Class A South Atlantic League, where he had a 5–6 win–loss record and a 2.62 ERA while recording 121 strikeouts in 106 1⁄3 innings pitched on the strength of his fastball. The Mets added Matz to their 40-man roster on November 20, 2013, to protect him from being selected in the Rule 5 draft. He began the 2014 season with the St. Lucie Mets of the Class A-Advanced Florida State League, where he had a 4–4 record and a 2.21 ERA in 69 1⁄3 innings pitched, before he was promoted to the Binghamton Mets of the Class AA Eastern League in 2014. With Binghamton, Matz pitched to a 6–5 record with a 2.28 ERA and 69 strikeouts in 71 innings. After the season, the Mets named Matz their Organizational Pitcher of the Year.
Matz opened the 2015 season with the Las Vegas 51s of the Class AAA Pacific Coast League. In 15 games started for Las Vegas, Matz had a 7–4 record and a 2.19 ERA.
The Mets promoted Matz to make his major league debut on June 28 against the Cincinnati Reds at Citi Field. Matz' first pitch was a wild pitch to Reds' leadoff hitter Brandon Phillips. Then on a 3–1 count to Phillips, he hit a home run off the left field fence, originally a single, but overturned on video review Matz became the second pitcher in Mets history to give up a home run to the first batter he faced since Jon Niese on September 2, 2008. Matz won his debut and, using a bat given to him by Las Vegas teammate Matt Reynolds, recorded four RBIS, breaking the Mets' franchise record for RBIs in a major league debut and setting an MLB record for most RBI by a pitcher in their debut. He was also the first Mets pitcher with four RBIs in any game since Dwight Gooden in 1990. He finished the game with three hits as the Mets went on to win, 7–2. Matz described pitching for the team that he grew up supporting as "a dream come true." Matz was the first pitcher from Long Island to make his MLB debut with the Mets since Ray Searage in 1981.
In his second start, Matz pitched six scoreless innings while striking out eight and allowing two hits. After the game, the Mets announced that Matz tore a latissimus dorsi muscle and would miss at least a month recovering. Matz returned to the Mets on September 6, starting at Marlins Park against Miami, and left the game with a blister and in line for a win, but received a no-decision. On September 18, Matz returned to Citi Field, pitching the first game of the Subway Series and earning a win. He allowed one run on seven hits and a walk in six innings while striking out four batters. With that, Matz became the first pitcher in franchise history to allow two earned runs or fewer in each of his first five career starts, according to the Elias Sports Bureau.
Matz finished the season with a 4–0 record in six starts with a 2.27 ERA in 35 2⁄3 innings pitched with a WHIP of 1.234 with 35 strikeouts while giving up 34 hits, 9 runs, 4 home runs, and 10 walks. Matz made his postseason debut in Game Four of the 2015 National League Division Series in a 3–1 loss to the Los Angeles Dodgers. Matz pitched five innings giving up 6 hits, 3 runs, 2 walks, and 4 strikeouts. In Game Four of the 2015 National League Championship Series against the Chicago Cubs he pitched 4.2 innings giving up 4 hits, 1 run, 2 walks, and 4 strikeouts. Matz started game four of the 2015 World Series against the Kansas City Royals pitching 5 innings giving up 7 hits, 2 runs, and 5 strikeouts. He received a no-decision as the Royals beat the Mets 5–3.
Matz made the Mets' Opening Day roster in 2016, as the fifth starter in the Mets rotation that consisted of Matt Harvey, Noah Syndergaard, Jacob deGrom, and Bartolo Colon. Matz made his first start on Monday Night Baseball against the Miami Marlins, but was shelled by Miami, only pitching 1.2 innings, and allowing 7 runs, taking the loss. However, after the bad loss, Matz rebounded to finish April strong, winning his next three starts in the month.
After compiling a 4-0 win-loss record, a 1.83 ERA, and 31 strikeouts in May, he was named the National League Rookie of the Month. However, after a great May, Matz pitched badly over the next two months, not winning a game and seeing his ERA ballon from 2.28 to 3.63. On June 28, it was revealed that Matz and teammate Noah Syndergaard had pitching most of the season with bone spurs in the back of their pitching elbows. It was indicated that Matz's spur was more significant and he will need to have it surgically removed. However, surgery would require a three-month recovery time, which would force Matz to miss the rest of the 2016 Season. Matz decided to wait until after the season for surgery to remove the bone spur.
After two rough months, Matz pitched well in August, striking out 9 in 6 innings against the Arizona Diamondbacks on August 9, and then taking a no-hitter into the 8th inning in his next start against the San Diego Padres. Matz struck out 8 batters in that game, and picked up his ninth win of the season, giving him a 9-8 win-loss record. Alexei Ramírez was the first Padre to hit against Matz in that game.
The Mets placed Matz on the 15-day disabled list on August 22, retroactive to August 15, citing "left shoulder tightness". On September 27, it was announced that Matz would undergo surgery for a bone spur in the left elbow, thereby ending his season.
Matz received one third place vote for the 2016 National League Rookie of the Year, placing him in a three-way tie for sixth place with Jon Gray and Seung-hwan Oh.
Matz began the 2017 season on the disabled list with an elbow injury, later labeled as a flexor strain irritation. He missed two months and was activated on June 9th, pitching his first game the following day. Matz battled through injury and inconsistency, pitching only in 12 games before being placed back on the disabled list with irritation in the ulnar nerve of his pitching elbow. On August 22, 2017, Matz underwent season-ending elbow surgery. Matz was given a PRP injection and told to rest when originally diagnosed with the elbow injury back in April; however, the Mets allowed Matz to skip his scheduled bullpen sessions in order to pitch through pain. Matz pitched 66 2⁄3 innings, with a 2–7 record and a 6.08 ERA.