He has previously played in MLB for the Baltimore Orioles, Arizona Diamondbacks, St. Louis Cardinals, and New York Mets.

[6] The Orioles traded fellow relief pitcher Luis Ayala in April 2013, further solidifying McFarland's hold on a roster spot and improving his chances of staying with Baltimore; a Rule 5 pick must remain with the MLB team that drafted him for the entire season or be offered back to the original team for $25,000.

He earned his first career major league win on June 13, pitching an inning of relief against the Boston Red Sox.

McFarland earned his first major league win as a starter on July 1, 2014, against the Texas Rangers.

[9] McFarland pitched in 30 contests for Baltimore in 2015, posting a 2-2 record and 4.91 ERA with 26 strikeouts over 40+1⁄3 innings of work.

[10] McFarland made 16 relief appearances for the Orioles during the 2016 campaign, but struggled to a 6.93 ERA with 7 strikeouts across 24+2⁄3 innings pitched.

[19] On February 16, 2021, McFarland signed a minor league contract with the Washington Nationals organization.

[22] He was assigned to the Triple-A Rochester Red Wings to begin the 2021 season, and logged a 5.25 ERA in 18 appearances before he was released on June 30.

[26] He was the losing pitcher in the NL Wild Card Game, surrendering a walk to Cody Bellinger, who later scored on Chris Taylor's tie-breaking walk-off home run.

[32] After clearing waivers, McFarland elected free agency in lieu of an outright assignment on July 18.

[35] On January 26, 2024, McFarland signed a minor league contract with the Los Angeles Dodgers that included an invitation to spring training.

[36] On March 26, the Dodgers traded him to the Athletics in exchange for cash consideration and he was added to the major league roster.