His son, Patrick, confirmed the death on Friday in an Instagram post. No cause of death was given.
O'Neal, also known for his long-time romance with the late actress Farrah Fawcett, revealed in 2012 that he had been diagnosed with prostate cancer, though he said then that his prognosis was good.
O'Neal, a Los Angeles native who trained as an amateur boxer before taking up acting, made his showbiz breakthrough in 1964 when he landed a role in the hit prime-time television soap opera Peyton Place.
He is perhaps best remembered for his Oscar-nominated star turn opposite Ali MacGraw in the 1970 romantic drama Love Story, a box office sensation adapted from Erich Segal's popular novel of the same title.
He went on to star in What's Up, Doc? opposite Barbra Streisand, a 1972 screwball comedy directed by Peter Bogdanovich, who also directed O'Neal in the 1973 film hit Paper Moon, which co-starred the actor's then-young daughter.
Her debut role in the Depression-era drama as a precocious, cigarette-smoking orphan earned Tatum O'Neal an Academy Award at the age of 10 for best supporting actress.
She claimed in a 2004 memoir that she suffered years of parental abuse and fits of jealousy from her father, and that he had introduced her to drugs, leading to an estrangement of nearly 25 years.
Ryan O'Neal disputed his daughter's claims, and the two eventually reconciled, appearing in a biographical docuseries together in 2011 called Ryan and Tatum: The O'Neals.
"My dad passed away peacefully today, with his loving team by his side supporting him and loving him as he would us," her half-brother, Patrick O'Neal, wrote on Instagram on Friday in a tribute, adding that his father "has always been my hero."
