Police say no foul play is suspected in connection with the death.
The body was located in the parking garage at the corner of C and Third streets around 7:30 a.m., Sgt. Raul Aguilar said.
Aguilar said the body was found on the ground inside the garage, which was shut down as police conducted an investigation this morning.
The garage reopened around 10 a.m.
The Marin County coroner's office is set to perform an autopsy on the body on Monday to determine the cause of death.