The Kansas City Royals selected Farrell in the sixth round of the 2013 MLB draft. Farrell made 10 starts with Rookie Advanced level Idaho Falls, where he went 1–3 with a 6.65 ERA, although he did strike out 45 batters in 43 innings. Farrell's struggles continued in 2014 with Single-A Lexington, going 2–12 in 19 starts with a 5.25 ERA while striking out 8.5 batters per 9 innings. Farrell opened the 2015 season with High-A Wilmington, then was promoted to Double-A Northwest Arkansas in May. Farrell made 16 starts at Double-A, going 5–3 with a 3.09 ERA, although his K/9 dropped to 6.3. Farrell pitched 2016 with Triple-A Omaha, where in 19 appearances, he went 6–3 with a 3.76 ERA. He returned to Omaha to begin the 2017 season, where he made 13 starts before earning a promotion to the major leagues on July 1. When the Royals needed a starting pitcher for the first game of a doubleheader against the Minnesota Twins, Farrell was called up from Omaha to make his major league debut. He gave up 5 runs in 2 innings and left the game as the pitcher of record, but did not receive a loss as Kansas City came back to win the game. Originally recalled as the 26th player for the doubleheader, Farrell was optioned back to Omaha the next day. Following the Royals' acquisition of three major league pitchers from the San Diego Padres, Farrell was designated for assignment on July 24.
Farrell was traded to the Los Angeles Dodgers in exchange for cash considerations on July 28, 2017, and was assigned to the Triple-A Oklahoma City Dodgers. Farrell made one appearance for Oklahoma City, giving up 2 earned runs in 4 innings.
Cincinnati Reds
On August 9, 2017, Farrell was claimed off waivers by the Cincinnati Reds, and assigned to the Triple-A Louisville Bats. He was called up by the Reds on August 23, when he made his National League debut and pitched 3 innings of scoreless relief.
Chicago Cubs
Farrell was claimed off waivers by the Chicago Cubs on October 4, 2017. He pitched five shutout innings on June 2, 2018 against the New York Mets. On June 24, 2018, Farrell was assigned to the Triple-A Iowa Cubs. He was designated for assignment on September 1, 2018. He finished 3-4 in 20 games. He struck out 39 batters in innings.
Farrell was claimed off waivers by the Los Angeles Angels on September 3, 2018. On December 21, 2018, Farrell was designated for assignment by the Angels.
Texas Rangers
On January 4, 2019, Farrell was claimed off waivers by the Texas Rangers. On March 2, 2019, Farrell was struck in the face by a line drive during a spring training game and suffered a broken jaw and a concussion. Farrell underwent surgery on March 6th to insert a plate and screws on the jaw bone. His jaw was wired shut and he was placed on a liquid diet for one month. Farrell lost 15-20 pounds during the recovery process. He was placed on the 60-day injured list to open the 2019 season. Farrell rehabbed with the AZL Rangers and Frisco RoughRiders before being activated on August 23. In 9 games for Texas in 2019, he went 1–0 with a 2.70 ERA over innings.
Personal life
Luke Farrell is the youngest of three sons born to former Boston Red Sox manager John Farrell. John Farrell took a one-day leave from the Red Sox to be at Kaufmann Stadium on July 1, 2017, to watch Luke make his MLB debut; the Red Sox were managed that day by bench coachGary DiSarcina. On September 23, 2017, Luke pitched a scoreless inning of relief against the Red Sox, which was the first time in MLB history that a son pitched against a team managed by his father. Luke's brothers, Jeremy and Shane, were both selected in the MLB Draft, with Jeremy playing in the minor leagues from 2008 through 2015.
