He played all or part of nine seasons in Major League Baseball for the Montreal Expos (1984–88), Cincinnati Reds (1988), Minnesota Twins (1989), Atlanta Braves (1991–92) and Toronto Blue Jays (1994) as a relief pitcher.

He made one World Series appearance with the Braves in 1991, pitching the 9th inning of a Game 5 blowout win.

He worked as pitching coach for the Montreal Expos/Washington Nationals and Miami Marlins before being hired by the Blue Jays organization.

St. Claire worked seven years as the pitching coach for the Montreal Expos, later the Washington Nationals.

On January 13, 2014, St. Claire was named as the pitching coach for the Toronto Blue Jays Triple-A affiliate Buffalo Bisons.