Matthew J. Thornton (born September 15, 1976, in Three Rivers, Michigan), is a left-handed Major League Baseball relief pitcher for the Chicago White Sox. Before the 2006 season, Thornton was with the Seattle Mariners.
In the 1995 Major League Baseball Draft, Thornton was drafted by the Detroit Tigers in the 27th round but decided not to sign with them. Thornton played college baseball for Grand Valley State University and was drafted by the Seattle Mariners in the first round as the 22nd overall pick in 1998 Major League Baseball Draft.
Thornton played briefly (only pitched 1 inning) with the Single A Everett AquaSox in the Northwest League. In 1999 and 2000, Thornton was a starting pitcher with the Wisconsin Timber Rattlers in the Midwest League and showed improvement with his ball control and accuracy, striking out nearly 1 batter an inning. 2001 was probably Thornton's breakout year. Thornton started for San Bernardino Stampede in the California League (high-A ball) and had a 14–7 record, along with a stellar 2.52 ERA and 192 strikeouts in only 157 innings pitched.