John Travolta said he nearly retired from films after the death of his teenage son three years ago.
Sixteen-year-old Jett died after suffering a seizure on a family holiday in the Bahamas.
Travolta, who shot to fame in Saturday Night Fever in 1977, said he agreed to star in Oliver Stone's new film Savages because it was a "high-end, five-star film".
He told BBC Breakfast: "I lost my son a few years ago and I had been having quite a time of that and after three years getting a lot of support from my church and a lot of support from people, fans, family, I decided that it was okay to go back to work because I'd even thought of retiring at one point because it felt like too much."
Travolta also called for a privacy law and condemned the publication of topless photographs of the Duchess of Cambridge.
The actor, who famously danced with Diana, Princess of Wales at a White House dinner in 1985, said it was the "worst time to be famous".
He said: "There is a right to privacy whether you're famous or not famous and I feel that anyone being invaded at that level is unfortunate and there should be a law, no one would like that."
The film, which opens in the UK on Friday, is based on Don Winslow's best-selling thriller and also stars Blake Lively, Salma Hayek and Benicio del Toro.