He played in Major League Baseball (MLB) for the Boston Red Sox, Detroit Tigers and Milwaukee Brewers.

On December 11, 2014, the Red Sox traded Wilson along with Gabe Speier and Yoenis Céspedes to the Detroit Tigers for Rick Porcello.

[9] On May 27, 2015, Alex Wilson made his first career major league start for the Detroit Tigers, against the Oakland Athletics, throwing 52 pitches in 3 scoreless innings.

On July 30, 2015, Wilson earned his first major league save, getting the final five outs in a 9–8 Tigers win over the Baltimore Orioles.

[10] For the season, he pitched 70 innings (including a team-high 67 in relief), with 16 games finished, 2 saves, a 2.19 ERA and a 1.03 WHIP.

During the 2016 season, Wilson set career highs with 62 appearances and 73 innings, while posting a 4–0 record with a 2.96 ERA, with 49 strikeouts and 21 walks.

[11] On August 25, Wilson was ejected for the first time in his Major League career after hitting Todd Frazier with a pitch.

[12] On September 23, 2017, Wilson sustained a non-displaced fractured right fibula after he was hit by a line drive off the bat of Joe Mauer, ending his season.

[15] In a game on May 7, 2018, Wilson hurt his foot covering first base, and was later diagnosed with a plantar fascia strain.

He opted out of his contract with the Indians on March 21, 2019, after being informed he would not make the opening day major league roster.

[22] On January 4, 2020, Wilson signed a minor league contract with the Detroit Tigers that included an invitation to spring training.

Wilson announced his retirement from professional baseball on July 28, 2020, and joined the Ballengee Group as an advisor.