Giolito attended Harvard-Westlake School in Studio City, California, and was selected by the Nationals in the first round in the 2012 MLB draft.

He was part of a Harvard-Westlake baseball team that included Max Fried and Jack Flaherty, with Ethan Katz as their pitching coach.

[3][4] In March 2012, his senior year, Giolito sprained the ulnar collateral ligament in his right elbow, sidelining him for the rest of his high school season.

[15] By the end of the month, the team had scheduled Tommy John surgery to repair his injured elbow ligament.

He was promoted to the Auburn Doubledays of the Class A-Short Season New York–Penn League, and allowed one earned run in the 16 innings he pitched.

[13] In 2014, Giolito played his first full season of professional baseball with the Hagerstown Suns of the Class A South Atlantic League.

[20] On June 28, 2016, the Nationals added Giolito to their active roster and he made his major league debut that night against the New York Mets.

[21] On December 7, 2016, the Nationals traded Giolito, Reynaldo López, and Dane Dunning to the Chicago White Sox for Adam Eaton.

[29] On September 16, 2019, the White Sox shut down Giolito for the rest of the season due to a mild lat strain in his pitching arm.

He struck out 13 batters and threw 74 of 101 pitches for strikes; a fourth-inning walk to Erik González was the only blemish in an otherwise perfect game.

On January 13, 2023, Giolito signed a one-year, $10.4 million contract with the White Sox, avoiding salary arbitration.

[37] He made his first start for the Guardians on September 4, and became the first pitcher to surrender eight earned runs in a game for three different MLB teams in the same season since Bill Magee in 1899.

On January 3, 2024, Giolito signed a one-year contract with the Boston Red Sox, with a player option after the first season.

[39] In early March, Red Sox manager Alex Cora stated that Giolito would miss the start of the season due to discomfort in his right elbow.

Lucas’ brother Casey is an actor, while his uncle, Mark Frost, is a novelist, television screenwriter, and producer best known as the co-creator of Twin Peaks with David Lynch.