Brandon James Lyon (born August 10, 1979) is an American former professional baseball pitcher.

He played in Major League Baseball (MLB) for the Toronto Blue Jays, Boston Red Sox, Arizona Diamondbacks, Detroit Tigers, Houston Astros, and New York Mets.

Lyon made his major league debut halfway through the 2001 season, posting a five-win, four-loss record for the Toronto Blue Jays, with a 4.29 ERA from 11 starts.

Lyon missed the entire 2004 season due to injury, after having been traded along with Casey Fossum, Michael Goss and Jorge de la Rosa to Arizona in exchange for Curt Schilling.

Lyon improved in 2005, converting 14 saves in 15 opportunities while pitching in 32 games and spending part of the season as the Diamondbacks' closer, replacing the injured José Valverde.

Lyon found his niche as the Diamondbacks' primary setup man, pitching in front of Valverde, as Arizona won the NL West division title.

On February 10, 2014, Lyon signed a minor league contract with the Los Angeles of Anaheim.

Lyon used an arsenal of five pitches: a four-seam fastball at 90–92 mph, a two-seamer at 90–91, a cutter at 89–91, and a curveball at 78–80.