Police said they discovered the 40-year-old actor's body around 4 p.m. Lt. Frank Fabrega said there were no obvious signs of foul play.
Sean Penn's publicist, Mara Buxbaum, issued a statement saying that "the Penn family would appreciate the media's respect of their privacy during this difficult time."
Chris Penn's body was found inside the four-story condominium complex after police were called by someone from within the building, Fabrega said.
Penn's body was discovered in a bed inside the residence, located in a four-story condominium complex near the beach on Ocean Avenue in Santa Monica, said Capt. Ed Winter of the county coroner's office. Authorities were called to the condominium complex by Penn's housekeeper, Winter said.
An autopsy will be conducted to determine the cause of death, authorities said.
Chris Penn's credits included "Mulholland Falls," "Rumble Fish," "All the Right Moves," "Footloose" and "Rush Hour." He also played Nice Guy Eddie Cabot in the 1992 Quentin Tarantino crime drama "Reservoir Dogs."
His late father, Leo Penn, directed television shows. His mother, Eileen Ryan, is an actress whose credits include "I Am Sam," "Magnolia" and "Parenthood." Another brother is musician Michael Penn.
Chris Penn's latest film, "The Darwin Awards," was scheduled to premiere Wednesday at the Sundance Film Festival.