He played as a catcher in Major League Baseball for the Toronto Blue Jays (1995-1997), Chicago Cubs (1998-1999), Florida Marlins (2000), Montreal Expos (2001), Cleveland Indians (2004), and Boston Red Sox (2004).

Martínez was signed by the Toronto Blue Jays as an amateur free agent in 1990 and made his Major League Baseball debut at the age of 24 on June 24, 1995.

He spent most of the season with Cleveland's Triple-A affiliate, the Buffalo Bisons, playing one game for the Indians major league team.

On August 31, 2004, Martínez's contract was purchased by the Boston Red Sox, where he played three games before being granted free agency at the end of the season.

On December 14, 2005, Martínez signed a minor league contract with the New York Mets, playing 85 games for their Triple-A affiliate, the Norfolk Tides, and becoming a free agent at the end of the season.