He played in Major League Baseball (MLB) for the Minnesota Twins, Cleveland Indians, New York Yankees, Chicago White Sox, Milwaukee Brewers, New York Mets, Seattle Mariners, Atlanta Braves, Arizona Diamondbacks, and Kansas City Royals.

[12] Swarzak was one of the top rated prospects in the Twins' farm system before a fifty-game suspension for violation of Minor League drug policy on April 20, 2007, sidetracked his career.

[14][15] After having started the season with the Double A New Britain Rock Cats, upon his reinstatement from the restricted list on June 11, he was reassigned to the Class A Advanced Fort Myers Miracle.

[18][19] After a line drive broke his foot,[20] Swarzak's 2010 season was statistically awful as he spent the whole year in the minors.

In 2012, Swarzak started five games for the Twins while making 39 appearances out of the bullpen, pitching to a collective 96 innings of work.

[24] On January 15, 2015, Swarzak signed a minor league contract with the Cleveland Indians that included an invitation to Spring Training.

[36] On July 25, 2017, Swarzak was traded by the Chicago White Sox to the Milwaukee Brewers for outfielder Ryan Cordell.

[38] On April 3, the Mets placed Swarzak on the disabled list with an oblique strain and recalled Hansel Robles.

[39] Swarzak was activated from the disabled list on June 5 after appearing in three rehab games with the Triple-A Las Vegas 51s.

[40] On December 3, 2018, the Mets traded Swarzak, Jay Bruce, Jarred Kelenic, Gerson Bautista, and Justin Dunn to the Seattle Mariners for Edwin Díaz, Robinson Canó, and $20 million.

On March 4, 2021, Swarzak signed a minor league contract with the Arizona Diamondbacks organization that included an invitation to Spring Training.

[50] On May 14, 2021, Swarzak signed a minor league contract with the Kansas City Royals organization and was assigned to the Triple-A Omaha Storm Chasers.

[51] On June 18, Swarzak was selected to the active roster[52] and made his Royals debut the following day against the Boston Red Sox, pitching for his tenth major league team.