A lifeguard on duty reportedly saw the man struggling in a no-swimming area next to a rock groin at 39th Street, according to the beach patrol.
Authorities said that the man was found unconscious in the water near 39th and Seawall on Saturday.
Beach patrol says he was taken by ground ambulance to the trauma center at UTMB Health's John Sealy Hospital, where he later was pronounced dead while being treated.
The man's death marks the first fatal drowning on a Galveston beach this year.