The collision was reported at 9:14 p.m. near the intersection of Sunset Boulevard and Irving Street.
The pedestrian, a 26-year-old man, was struck while walking west across Sunset Boulevard outside of a crosswalk, police spokesman Officer Gordon Shyy said.
He suffered a broken pelvis and lacerated liver and was taken to San Francisco General Hospital to be treated for his injuries, which are considered life-threatening, Shyy said.
The driver, a 66-year-old man, who had been traveling south on Sunset, remained at the scene after the collision. He was released after being interviewed by police, and neither alcohol nor drugs are believed to have been a factor in the accident, according to Shyy.
Anyone with information about the collision is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.