It happened about a half mile from 13 Mile Road around 11:24 a.m., Jamaica Beach Fire Chief Kyle Baden said.
The man's body was found after about two hours of searching. Officials said his body was found in knee-deep water. They did not identify the man or say where he was from.
Officials said the man was in his late 60s.
He is the fifth person to drown along the beaches of Galveston Island this year.
Officials warned that the recent hurricanes and tropical storms generated surge and high tides that gouged the sea floor and created unexpected drop-off points.