During the 1960s, he became more politically active and worked on Robert F. Kennedy's Democratic presidential campaign. He was present at the Ambassador Hotel in Los Angeles at the time of Robert Kennedy's assassination in June 1968. During the same year, he discovered the woman who had raised him was his grandmother, not his mother as he thought, and learned that the woman he thought was his sister was actually his mother. Those events deeply affected Darin and sent him into a long period of seclusion.
Although he made a successful comeback (in television) in the early 1970s, his health was beginning to fail following bouts of rheumatic fever in childhood. The knowledge of his vulnerability had always spurred him on to use his musical talent while still young. He died at the age of 37 after a heart operation in Los Angeles in 1973.