Leiter has five pitches: fastball, cut fastball, slider, change, and a sinking fastball which is almost unhittable both by right and left batters. He needs to continually change speeds and stay ahead of the hitter to be successful. Leiter keeps baserunners off balance by using an assortment of pickoff moves and a short delivery, but he has problems controlling the running game. Once he's committed to throwing a pitch, he is so slow to the plate that his catchers usually don't have a chance. As a fielder, his quick feet allow him to move off the mound and field the ball with relative ease.

In 19 seasons, Leiter compiled a 162-132 record with 1974 strikeouts, a 3.80 ERA, 16 complete games, 10 shutouts, and 2391.0 innings in 419 games. In 17 post-season games he went 1-3 with 66 strikeouts and 4.50 ERA.

Following the 2004 season, the Mets declined Leiter's US$10 million option for 2005, making him a free agent. His old team, the Marlins, signed Leiter to a one-year, $8 million contract on December 8, 2004.

Leiter struggled during his return to the Marlins. His cut fastball was flattening out, and he walked more batters than usual (60 in 80 innings, to go with 88 hits. In 17 appearances (16 starts), he had a 3-7 record and a 6.64 ERA, and he took much criticism for the Marlins' first-half struggles in 2005 (they were expected to win their division but remained 7 games behind the Washington Nationals at the All-Star break). He was demoted to the bullpen in late June, but he returned to the rotation after an injury to Josh Beckett. On July 10, when the Marlins played their last game before the three-day All-Star break, he gave up six runs in three-plus innings.

On July 14, 2005, the Florida Marlins designated Leiter for assignment. The next day, he was acquired by the New York Yankees, who had four starting pitchers on the disabled list, for a player to be named later. His first start as a Yankee since April 26, 1989, came on July 17, 2005, against the division-leading Boston Red Sox. Leiter won the game, pitching 6 1/3 innings, allowing one run and three hits, and striking out eight. After several starts, some good, some bad, he informed Joe Torre that he would be willing to pitch out of the bullpen, where he would stay for the latter part of the season, yielding his starting slot to Aaron Small.

Leiter signed a minor league contract with the Yankees in 2006; however, he stated he would likely retire. After the World Baseball Classic, he officially retired in an interview on the Yankees Entertainment and Sports Network(YES), after a Yankees spring training victory versus the Indians where Leiter pitched 1/3 an inning.

Leiter has worked in the broadcast booth for FOX during the playoffs in the past several seasons, mainly to provide in-depth analysis of various pitchers.