He succeeded Buck Martinez on June 3, 2002, served the entire 2003 season, then was replaced by John Gibbons on August 8, 2004, after compiling a 191–191 win–loss record (.500).

Tosca managed in the farm systems of the New York Yankees, Kansas City Royals, Florida Marlins and Atlanta Braves for 17 seasons between 1980 and 2001.

He has managed at the highest level of minor league baseball with the Triple-A Charlotte Knights (1997) and Richmond Braves (2001), and was the bench coach on Buck Showalter's staff during the first three MLB seasons (1998–2000) in Arizona Diamondbacks history.

Tosca was hired as the third base coach of the Blue Jays for the 2002 season by the club's recently appointed general manager, J. P. Ricciardi.

Over the final two-thirds of the campaign, Tosca led the Jays to a 58–51 (.523) mark and a third-place finish in the American League East Division.