Harold "Hal" Gilson (February 9, 1942 – June 20, 2022) was an American Major League Baseball pitcher who played for the St. Louis Cardinals and Houston Astros in 1968.

Nicknamed "Lefty", he was originally signed by the Chicago Cubs in 1961 and was traded to the Cardinals on April 7, 1965, with Bobby Pfeil for Bob Humphreys.

He made his big league debut on April 14, 1968, against the team with which he had originally signed, the Cubs.

Overall, Gilson allowed a hit and walked one in two innings in his big league debut, but did not give up a single run.

Harold Gilson died on June 20, 2022, in Scottsdale, Arizona, from a major stroke.