Walker played college baseball for the South Carolina Gamecocks and won the College World Series in 2010 and 2011. Walker was selected in the fourth round of the 2012 MLB draft by the Orioles and made his MLB debut with the team in 2014. He was later claimed off waivers in 2017 by the Diamondbacks and became their regular first baseman after Paul Goldschmidt was traded following the 2018 season. Walker is a three-time Gold Glove Award winner and helped the Diamondbacks win the National League pennant in 2023. After becoming a free agent following the 2024 season, he signed with the Astros.
On September 17, 2014, Walker was called up to the Orioles from the Triple–A Norfolk Tides.[11] He made his major league debut later that day. Facing Toronto Blue Jays pitcher J. A. Happ, Walker hit a double for his first major league hit.[12] On September 20, he had his first multi-hit game, including his first career major league home run, off Boston Red Sox starter, Rubby De La Rosa.[13]
On February 21, 2017, the Orioles designated Walker for assignment.[14]
Arizona Diamondbacks
On March 6, 2017, the Cincinnati Reds claimed Walker off waivers. The Atlanta Braves also put a waiver claim on Walker, but lost due to the order.[15]
Walker was called up again and played in 11 games in 2017 for the Diamondbacks, batting .250 with 2 homers. He played in 37 games in 2018, for a .163 average with 3 home runs.
In 2019, Walker hit .259/.348/.476 with 29 home runs and 73 RBIs. He had a 9 Defensive Runs Saved (DRS) rating, the best in the National League among first basemen, and led all major league first basemen with 139 assists.[17][18] In the pandemic-shortened 2020 season, he hit .271/.333/.459 with 7 home runs and 34 RBIs.
In 2021, Walker batted .244/.315/.382 with 10 home runs and 46 RBIs in 115 games. The following year, he hit a career-high 36 home runs and drove in 94 RBI while winning his first career Gold Glove Award.[19]
On January 13, 2023, Walker agreed to a one-year, $6.5 million contract with the Diamondbacks, avoiding salary arbitration.[20] He finished the season batting .258/.333/.497 with 33 home runs and a career-high 103 RBI in 157 games played. He also helped lead the Diamondbacks to the 2023 World Series, where they lost to the Texas Rangers in five games.[21] After the season, he won his second consecutive Gold Glove Award.[22]
Walker played in 130 games for the Diamondbacks in 2024, batting .251/.335/.468 with 26 home runs and 84 RBI.[23] He won the Gold Glove Award for the third straight year.[24]
Houston Astros
On December 23, 2024, Walker signed a three-year, $60 million contract with the Houston Astros.[25]