The actor, who was Oscar nominated for his role in the 1978 Vietnam War movie, was a last-minute addition to the film - and feels he was only asked to take part because he was a neighbour of Schlesinger's replacement Hal Ashby.
Dern tells WENN Pacino and Schlesinger walked away from the film after two days of shooting, leaving producer Jerome Hellman desperate to replace them in less than a week - or risk studio bosses scrapping the project.
Dern recalls, "Jerry Hellman lived in Malibu Colony; I lived in Malibu Colony and Hal Ashby lived in Malibu Colony. Jerry went to Hal, gave him the script for Coming Home and said, 'Can you shoot Thursday?' He said, 'It's Tuesday night!' He said, 'What's the rush if I started Monday?' Hellman said, 'The rush is two other movies about Vietnam started last week - Apocalypse Now and The Deer Hunter - but I don't have explosions or war in my script.
"He said, 'I got the word 'home', and United Artists will shut my movie down if we don't continue on.' So, in 36 hours, Hal went to work.
"Jon Voight, who was playing my role, went up and played Pacino's role, Luke Martin. I lived on the same street as Hal, so he said, 'What about the Dernster for Captain Bob?' So in I come. (Co-star) Jane Fonda went along with it because she was kind of the silent producer of the piece and we marched right on through."
The film was destined to be a great success - Fonda and Voight won Best Actress and Actor Oscars, and Nancy Dowd, Waldo Salt and Robert C. Jones shared the Best Screenplay prize.
Dern adds, "That was another twist - the three writers had never met each other. They all three wrote individual scripts. Nancy Dowd was hired by Jane Fonda, who gave her $25,000 to write a triangular love story set in Vietnam. Waldo Salt, who had written Midnight Cowboy with Jerry Hellman, wrote the screenplay and had a stroke and was in an oxygen tank and couldn't write anymore, so Bob Jones, who was the editor on Coming Home and had been in Vietnam, took over and became the scriptwriter.
"The day after the Oscars Jerry Hellman called Jane Fonda and says, 'Who's Nancy Dowd - because we just got a call from the Writers Guild saying she gets equal credit and equal money for the script because she won the Oscar. What do we do about her because she wants a piece of the movie?' Jane said, 'Oh God, I forgot to tell you - she wrote the script!'"