[5] The Oakland Athletics selected Muncy in the fifth round of the 2012 Major League Baseball draft.

[6] He made his professional debut with the Burlington Bees of the Single-A Midwest League, hitting .275 with four home runs in 64 games.

[7] Muncy began the 2015 season with the Nashville Sounds of the Triple-A Pacific Coast League (PCL), hitting .274 in 60 games.

[11] He made his debut as the starting third baseman against the Houston Astros and had one hit (a seventh inning single to center field off Scott Feldman) in four at-bats.

[12] On May 17, he hit his first major league home run off of Chicago White Sox pitcher Jeff Samardzija.

[25] After beating Javier Báez in the first round of the Derby, he lost to eventual champion Bryce Harper in the semi-finals.

[14] In the third game of 2018 World Series against the Boston Red Sox, Muncy scored the tying run in the 13th inning and then hit a walk-off home run in the 18th, concluding the longest game in World Series history after seven hours and 20 minutes.

In Game 3 of the 2020 NLCS, Muncy hit a grand slam off of Grant Dayton, capping off scoring 11 runs in the first inning.

[14] In the 2020 World Series, he batted .318 with one home run and six RBIs and helped the Dodgers win the championship.

[14] On May 30, 2021, Muncy hit his 100th career home run off of Zack Littell of the San Francisco Giants.

[14] In the final game of the regular season, Muncy dislocated his elbow when Jace Peterson of the Milwaukee Brewers collided with his arm while he was attempting to field the ball at first base, making him unavailable for the playoffs.

[14] Muncy remained the primary third baseman in 2023, playing in 135 games with a .212 batting average, 36 homers and a career-high 105 RBI.

[38] Muncy made his return on August 19 against the Seattle Mariners, hitting a two-run home run in the game.

[14] In Game 3 of the 2024 NLCS against the New York Mets, Muncy hit his 13th career post-season homerun, tying the Dodgers franchise record (previously set by Justin Turner and Corey Seager).