Farrell was a native of Seattle. He graduated from the University of Washington in 1956, served in the U.S. Army, and started his writing career at the Seattle Post-Intelligencer.

Farrell was hired by Time magazine in 1960, working first in San Francisco then in New York where he became the magazine’s music writer. He later served as Time’s correspondent in Paris and became a staff writer for its sister publication Life in 1968, where he wrote a column every other week, alternating with Joan Didion. He moved to Los Angeles in the early 1970s where he was West Coast Editor of Harper's. He also taught writing, including at the University of California, Santa Barbara.

He interviewed Buckminster Fuller for Playboy magazine in February 1972. He wrote Pat and Roald, the biographical story of author Roald Dahl and his wife actress Patricia Neal. A collection of his essays, How I Got to Be This Hip, edited by Steve Hawk, was published in 1999. He was a close friend of Joan Didion and her husband, John Gregory Dunne.

Barry Farrell died at age 49 in the Veterans Administration Hospital, West Los Angeles in 1984, after suffering a heart attack.