Bosio has served as a pitching coach in MLB for the Brewers, Tampa Bay Devil Rays, Chicago Cubs, and Detroit Tigers.

After playing for Rookie League and Class A Beloit Brewers teams through 1984, Bosio spent 1985 with the Double-A El Paso Diablos, compiling an 11–6 record in 28 games (25 starts).

In 1986, he spent most of the season with the Triple-A Vancouver Canadians, appearing in 44 games (all in relief); he had a 7–3 record with a 2.28 ERA in 67 innings pitched.

In seven seasons with the Brewers, Bosio appeared in 212 games (163 starts) with an overall record of 67–62, 749 strikeouts, 289 walks, and a 3.76 ERA in 1190 innings pitched.

On April 22, 1993, Bosio was the second pitcher in Mariners' history to pitch a no-hitter, when he retired 27 straight Boston Red Sox batters after walking the first two.

[5] The last out was made when shortstop Omar Vizquel bare-handed a high chopper over the mound by Ernest Riles and threw him out.

He started two games in the ALDS against the New York Yankees, pitching a total of 7+2⁄3 innings and giving up nine earned runs (10.57 ERA); he did not record a win or a loss.

In four seasons with the Mariners, Bosio appeared in 97 games (83 starts) with an overall record of 27–31, 310 strikeouts, 192 walks, and a 4.43 ERA in 520 innings pitched.

Bosio joined the Cincinnati Reds organization in 2008, serving as pitching coach at their Double-A Chattanooga Lookouts.

He was named to the same position for 2009 with the Carolina Mudcats, the Reds' new Double-A affiliate, but instead signed on with the Milwaukee Brewers' farm system.

Bosio joined the Chicago Cubs coaching staff before the 2012 season, as part of team president Theo Epstein's revamping of the organization.

[14] On November 2, 2017, Bosio was named the pitching coach for the Detroit Tigers under their new manager, Ron Gardenhire, for the 2018 season.

"[16] Bosio claimed that the offending comment was referring to relief pitcher Daniel Stumpf, who is white, as a "spider monkey"—due to the faces he makes while lifting weights—which was overheard and misunderstood by an African American clubhouse attendant.