A right-handed starting pitcher, Martínez played for the Baltimore Orioles (1976-1986), Montreal Expos (1986-1993), Cleveland Indians (1994-1996), Seattle Mariners (1997) and Atlanta Braves (1998).
In his 23-year career, Martínez had a 245-193 won-loss record with 2149 strikeouts, a 3.70 ERA, 30 shutouts, 122 complete games, four saves, and 3999 2/3 innings pitched in 692 games played (562 as starter). He is one of the top Latin American pitchers of all-time. On July 28 1991, he became the first Latin-born pitcher to throw a perfect game, the 13th in major league history, against the Los Angeles Dodgers.
On September 28, , Martinez won his 100th game for the Expos, becoming one of nine major league pitchers ever with at least 100 wins in both the American and National leagues. Others to do that are Jim Bunning, Ferguson Jenkins, Al Orth, Gaylord Perry, Kevin Brown, Randy Johnson, Nolan Ryan and Cy Young. On September 28, , Martínez was the last man to pitch to the late Hall of Famer Kirby Puckett in a regular-season game. A wild pitch by Martínez broke Puckett's jaw; the following spring during Grapefruit League spring training, Puckett developed glaucoma in his right eye and never played again. It was determined by team doctors that his broken jaw had no impact on his glaucoma. In fact, the pitch hit the left side of Puckett's face while the glaucoma was in Puckett's right eye.
In his post-playing career, Martinez has worked as a spring training instructor for the Baltimore Orioles in and , and currently serves as the pitching coach for the Palm Beach Cardinals.
The national baseball park in Managua (Nicaragua's capital city), Dennis Martínez National Stadium, was named in his honor.
Martinez runs his own organization, The Dennis Martinez Foundation, to help poor children around the world.
