The incident was reported at 9:03 p.m. on the Great Highway at Lawton Street, police said.
The pedestrian was crossing the Great Highway outside of a designated crosswalk when he was hit by a car heading north on the street, which runs along Ocean Beach, according to police.
The pedestrian, only identified as a male, was taken to San Francisco General Hospital with life-threatening injuries, San Francisco police spokesman Officer Albie Esparza said.
He remains in serious condition at the hospital this morning, Esparza said.
The driver stopped at the scene and has been cooperating with investigators, Esparza said.