After earning a bachelors' degree he joined the US Army Air Forces and served in the Korean War. He remained busy in movies during the 1960s and got highly praised for his performance. The movies like King Rat nad Assignment To Kill are the most remarkable movie of this actor. Later in the 1970s, he was more into television movies and stage program. He became an owner of the restaurant O Neals’ Ballon in his later days of life.
He got married to a Cynthi Baxter, an actress and together, they had two sons: Maximilian O'Neal and Fitzjohn O'Neal. During his active days in movies, he was engaged with different girls but was loyal to her wife and remained married with her until his death.
His net-worth has nOt been revealed even after his death. But it is for sure that he had collected a good amount of net worth from his successful acting career.
At the age of 66, he died because of his respiratory system failure. He was also suffering from tuberculosis and cancer.