[3] When he was two years old, his family moved from South St. Paul to Hollywood, California, where his father worked as a carpenter on film sets.

; and an ex-high school friend turned famous actor of Chet Kincaid in The Bill Cosby Show.

In 1970, he starred as one of the young doctors in the CBS prime-time series The Interns, in a cast led by Broderick Crawford.

In the early 1970s, Farrell guest-starred in the television Western drama Bonanza[5][6] and did a number of commercials as a spokesman for Maytag dryers and Plymouth automobiles, among other products.

Hunnicutt, along with series lead Harry Morgan, who was already signed to replace McLean Stevenson for the fourth season.

[7][8] Farrell hosted several National Geographic Presents specials and starred in a number of television films, including 1983's Memorial Day, which he co-produced.

In 2014 he was a supporting cast member on the Sundance TV Network criminal drama series The Red Road.

He portrayed Lee Miglin, a real estate baron who fell victim to serial killer Andrew Cunanan, in FX's anthology series American Crime Story: The Assassination of Gianni Versace.

Farrell was present as an observer for Amnesty International but was, in his words, "shanghaied into assisting with the surgery" when the doctor said his help was needed.

[17] In 2014, Farrell workshopped a play by George Shea that brought Charles David Keeling and his scientific work on atmospheric CO2 emissions to life.

[19] Farrell wrote an autobiography, Just Call Me Mike: A Journey to Actor and Activist (Akashic Books, ISBN 1-9333-5408-9), published in 2007.

The book covers his working-class childhood in West Hollywood, his break into show business, his personal life, and his increasing involvement in politics and the human rights movement in the United States, Cambodia, and Latin America.

In 1963, Farrell married actress Judy Hayden, who was working as a high school English and drama teacher in Laguna Beach, California.

Hunnicutt character, even though such a moustache below the upper lip was then, as now, a clear violation of Army uniform guidelines, especially when left untrimmed.

The normally clean-shaven Farrell grew it out for the character, as fashion trends at the time made the moustache in general popular for the first time since the beginning of the 20th century, due in part to fellow actors such as Burt Reynolds and Tom Selleck, as well as The Mustache Gang of the Oakland Athletics of Major League Baseball.