He has previously played in MLB for the Los Angeles Dodgers, Cincinnati Reds, and Minnesota Twins.

While at Marist, Farmer appeared in the film The Blind Side (2009), playing a high school quarterback.

[8] Farmer did not play in the game due to his subsequent promotion to the Double-A Tulsa Drillers of the Texas League.

[14] Two days later, in his first major league at bat, Farmer hit a walk-off two-run double off of Albert Suárez of the San Francisco Giants, in the bottom of the 11th inning, giving the Dodgers a 3–2 win.

[16] He made the Dodgers roster for the 2017 NLDS and 2017 NLCS, having four at bats as a pinch hitter, without recording a hit.

On December 21, 2018, the Dodgers traded Farmer to the Cincinnati Reds, along with Yasiel Puig, Alex Wood, Matt Kemp, and cash considerations in exchange for Homer Bailey, Jeter Downs, and Josiah Gray.

[19] On August 5, manager David Bell announced that Farmer would be the starting third baseman moving forward, with José Barrero assuming everyday duties at shortstop.

[21] On January 13, 2023, Farmer agreed to a one-year, $5.5 million contract with the Twins, avoiding salary arbitration.

[25] On November 23, 2024, Farmer signed a one-year contract with the Colorado Rockies including a mutual option for 2026.