Yelich was born in Thousand Oaks, California, and attended Westlake High School. During his freshman year, he batted .373 with 25 hits and 16 strikeouts in 67 at bats. In his sophomore year, he batted .341 with 31 hits and 24 strikeouts in 91 at bats. During Yelich's junior year, he batted .489 with 46 hits and struck out 6 times. In his senior year, he batted .451 with 37 hits, nine strikeouts and nine home runs in 82 at bats. He was named Second Team All-American by Max Preps and was ranked 34 among the top 100 players in the nation in high school.
Yelich was offered a scholarship to play at the collegiate level with the Miami Hurricanes baseball team. However, he was drafted by the Marlins 23rd overall in the 2010 Major League Baseball draft and agreed to a $1.7 million signing bonus on August 17, shortly before the deadline to sign 2010 draftees was about to pass. Yelich played for the Gulf Coast League Marlins for six games, getting nine hits and seven strikeouts with a batting average of .375 before being advanced to Class-A. He played in six games for the Greensboro Grasshoppers in 2010, batting .348. In 2011, he batted .261 with 43 hits, six strikeouts and four home runs. Yelich was named the Marlins' Minor League Player of the Year in both 2011 and 2012.
On July 23, 2013, the Marlins promoted Yelich to the major leagues from the Double-A Jacksonville Suns. He had a fantastic 2014 season, batting .284 with 21 steals out of the leadoff spot for the Miami Marlins. He also won a Gold Glove Award in left field, becoming the franchise's youngest ever player and first outfielder to win the award. During the season, Yelich set a franchise record for fielding percentage in left field, at .996. He served as the final out of Jordan Zimmermann's no-hitter on September 28, 2014, when Steven Souza Jr. made a diving play to save the no-hitter.
Yelich and the Marlins finalized a seven-year, $49.57 million contract extension on March 22, 2015. He struggled to start the season, and was placed on the disabled list in April with lower back strain before making his return on May 8. His batting average reached a season low of .178 on May 22. In August, Yelich bruised his right knee and was again placed on the disabled list. Yelich had improved from his earlier offensive struggles and was hitting .275/.343/.376 with six home runs, 29 RBIs and 14 stolen bases up to that point in the season. Despite aggravating the injury shortly after his return, Yelich remained an active player for the quality of his bat. Near the end of the season, Yelich shared the field with Marcell Ozuna, the outfielder who had replaced him during his second stint on the disabled list. Yelich closed the 2015 season with a .300 average. For the season, he had the highest ground ball percentage (62.5%), and the lowest fly ball percentage (15.0%), of all major league hitters.
Yelich was projected to bat third to start 2016. He hit well in that spot, and managed to increase his power output. On April 23, in a game against the San Francisco Giants, Yelich hit three doubles, which tied a franchise record. Defensively, Yelich was a starting outfielder, alongside Ozuna and Giancarlo Stanton. In late May, Yelich missed some time due to back spasms. After Stanton was placed on the disabled list, Ozuna played Stanton's usual position in right field, while Yelich took Ozuna's spot in center on days that backup outfielder Ichiro Suzuki was unavailable.
On March 31, 2019, Yelich became the sixth player in MLB history to hit a home run in each of his team's first four games.
On July 1, 2019, Yelich became the first player in Brewers franchise history to reach 30 home runs before the All-Star Break, beating former Brewer Prince Fielder's record of 29 home runs. Yelich was selected to participate in the Home Run Derby but had to withdraw due to a back injury. He was replaced by Matt Chapman in the Home Run Derby. On September 10, 2019, Yelich hit a foul ball off his kneecap and left the game. Shortly thereafter, it was revealed that his right kneecap was fractured, which prematurely ended his 2019 season.
In 2019, Yelich won his second National League batting title. He batted .329/.429 (leading the NL)/.671 (leading the major leagues) with a 1.100 OPS (leading the majors), 44 home runs (4th in the NL), 11.1 at bats per home runs (leading the league), a .342 ISO (leading the NL), 30 stolen bases (3rd), a 93.75 stolen base percentage (3rd), and 97 RBIs in 130 games. He had the highest Hard Contact Percentage of all National League batters, at 50.8%.