O'Hara was born in the Dublin suburb of Ranelagh in 1920, and is famous for being film actress and singer. The famously red-headed O'Hara has been noted for playing fiercely passionate heroines with a highly sensible attitude. She often worked with director John Ford and longtime friend John Wayne.

O'Hara is probably most famous for her role as Mary Kate Danaher in the 1952 film The Quiet Man. Set in 1930s Ireland, Sean Thornton (John Wayne), an Irish-born American from Pittsburgh, returns to Ireland to reclaim his family's farm in Innisfree. He meets and falls in love with the fiery Mary Kate Danaher, the spinster sister of the bullying, loud-mouthed landowner "Red" Will Danaher.

O'Hara was named Irish America magazine's "Irish American of the Year" in 2005. in 1991, she was given the Heritage Award by the Ireland-American Fund.

For her contributions to the motion picture industry, O'Hara has a star on the Hollywood Walk of Fame at 7004 Hollywood Blvd. In 1993, she was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma. She was also awarded the Golden Boot Award.

In March 1999, O'Hara was selected to be Grand Marshal of New York City's St. Patrick's Day Parade. In 2007, she wrote the foreword for the biography of her dear friend, actress Anna Lee.

In 2004, O'Hara released her autobiography 'Tis Herself, published by Simon & Schuster. In the same year, she was honored with a Lifetime Achievement Award from the Irish Film and Television Academy in her native Dublin.