The victim was helping the truck back up in the area of Marine Parkway and Twin Dolphin Drive just after 3 p.m., police said.
He was then struck by the dump truck as it was backing up on the side of the road and was taken to a local hospital where he was pronounced dead, according to the Police Department and the county medical examiner's office.
The medical examiner's office has identified the victim as Jose Villaneuva of Newark.
The cause of the crash remains under investigation.
Anyone with additional information regarding the case is asked to call Redwood City police at (650) 780-7100.