Happ was considered one of the top prospects for the2015 Major League Baseball draft.[7][8] TheChicago Cubs selected him in the first round, with the ninth overall selection.[9] Happ became the 50th player drafted from the Cincinnati Bearcats; 2008 picksJosh Harrison (6th round) andTony Campana (13th round) also both played for Cincinnati and were drafted by the Cubs, and former Bearcat and MLB 3-time All-StarKevin Youkilis is the Cubs Scouting and Player Development consultant.[10]
Happ began the 2017 season with theIowa Cubs of theClass AAAPacific Coast League. The Cubs promoted Happ to the major leagues on May 13.[19] In 26 games for Iowa prior his promotion, he was batting .298 with nine home runs and 25 RBIs.[20] He made his debut the same day he was called up, and hit a 413-foot home run off ofCarlos Martínez of theSt. Louis Cardinals for his first career MLB hit.[21][22] In a June 13 game atCiti Field against theNew York Mets, Happ became the fifth player in MLB history to hit agrand slam and strike out four times in the same game.[23] After Happ's 10th home run of the season, Cubs managerJoe Maddon said, "When he hits it, it goes quickly."[24] Happ hit his 20th home run on August 30 againstPittsburgh Pirates starterIván Nova.[25] He hit his 23rd on September 28 and his 24th the following day which was the second-most for a rookie switch-hitter in National League history.[26] He was third among NL rookies with 67 RBIs. Happ spent the remainder of the 2017 season with the Cubs after his June 13 promotion, and in 115 games, he slashed .253/.328/.514 with 24 home runs and 68 RBIs.
On the March 29, 2018, opening day game against theMiami Marlins, Happ hit a home run off ofJose Urena on the first pitch, becoming the second player in MLB history to hit a home run off the first pitch of an MLB season.[27] He finished the season slashing .233/.353/.408 with 15 home runs and 44 RBIs in 142 games, striking out 167 times.[28]
Happ was optioned to theIowa Cubs to begin the 2019 season, after slashing .135/.196/.192 during 17 spring training games, to work on cutting down his strikeout rate.[29] Happ was recalled to the majors on July 25, 2019. Happ finished the season with 11 home runs and 30 RBIs. He slashed .297/.409/.622 in 58 games, striking out 39 times. He was named National League Player of the Week on September 30, 2019.[30]
Happ started theCOVID-19-shortened2020 season in center field for the Cubs. He hit .258/.361/.505 with 12 home runs and 28 RBIs in 57 games.
Eligible forsalary arbitration in 2021, Happ filed for a $4.1 million salary, and the Cubs countered with a proposal of $3.25 million. Happ won the hearing.[31] In 2021, Happ hit .226/.323/.434 in 148 games for the Cubs. He led the team with 66 RBIs and set career highs with 105 hits, 25 home runs, 63 runs scored, and 9 stolen bases.
Happ and the Cubs agreed on a $6.85 million salary for the 2022 season.[32] In 2022, Happ finished the season with a career-high 158 games played, hitting .271/.342/.440 with 17 home runs, 72 RBIs, 72 runs, and 42 doubles. He made his first All-Star game and on defense won aGold Glove Award in left field.[33]
In his final season of arbitration, Happ and the Cubs agreed to a $10.85 million salary.[34] On April 13, 2023, Happ signed a three-year, $61 million contract extension with the Cubs.[35]
In 2021, Happ invested inJomboy Media, a digital media company that produces content focused on sports and pop culture. As part of the investment, Happ agreed to host his podcast,The Compound, on the Jomboy Media network.[40][41]
Happ and girlfriend, Julie Mazur, got engaged in May 2022.[42] They were married on November 18, 2023.[43]
