Farrell is scheduled to start the first game of the Royals' doubleheader against the Minnesota Twins.
A 2013 sixth-round draft pick out of Northwestern, Farrell had a 3.83 ERA in 82⅓ innings with 77 strikeouts for Kansas City's AAA Omaha Storm Chasers.
He was 2-0 with a 1.29 ERA in his two starts from June 19 through Monday, yielding just six hits and no walks while striking out a league-best 18 batters.
The major league start is a milestone for Farrell, who has had a long and complicated journey to the majors.
In 2009, when he was 18 and his father was the pitching coach for the Red Sox, Luke had surgery to remove a golf ball-sized tumor in his neck. The tumor was not cancerous, but its location could have affected nerves that control movement in the face, arm, tongue, lips and eyes.
Two years later, while Farrell was pitching in the Cape Cod League, the tumor returned. It was removed again.
But last year, Farrell had a five-year scan and there was no sign of the tumor.