Marlo Thomas was born on November 21, 1937, in Detroit, Michigan, the eldest child of comedian Danny Thomas (1912 – 1991) and his wife, the former Rose Marie Cassaniti (1914 – 2000). She has a sister, Terre, and a brother, Tony Thomas, who is a television and film producer. Her father was a Roman Catholic Lebanese American and her mother was Sicilian American. Her godmother was Loretta Young.

Thomas appeared in many television programs including Bonanza, McHale’s Navy, Ben Casey, Arrest and Trial, The Joey Bishop Show, The Many Loves of Dobie Gillis, My Favorite Martian, 77 Sunset Strip, and The Donna Reed Show, among others. Her big break came in 1965 when she was cast by Mike Nichols in the London production of Neil Simon’s Barefoot in the Park, co-starring Daniel Massey, Kurt Kasznar, and Mildred Natwick. (In 1986, she was once again cast by Nichols on Broadway in Andrew Bergman’s Social Security, co-starring Ron Silver and Olympia Dukakis.)

Thomas starred in an ABC pilot called Two’s Company in 1965. Although it did not sell, it caught the attention of an ABC programming executive. He met with Thomas, and expressed interest in casting her in her own series. With their encouragement, Thomas came up with her own idea for a show about a young woman who leaves home, moves to New York City, and struggles to become an actress. The network was initially hesitant, fearing audiences would find a series centering on a single female uninteresting or unrealistic.

In 1971, Thomas chose to end the series after five years. Both ABC and the show’s sponsor, Clairol, wanted the series finale to be a wedding between the two central characters, but Thomas rebuffed them, saying that she felt it was the wrong message to send to her female audience, because it would give the impression that the only happy ending is marriage. That Girl has since become popular in syndication.

In 1972, she released a children’s book, Free to Be… You and Me, which was inspired by her young niece Dionne Gordon. She went on to create multiple recordings and television specials of and related to that title: Free to Be… You and Me (1972, 1974) and Free to Be… A Family (1987), with Christopher Cerf. Also in 1972, she served as a California delegate to the Democratic National Convention in Miami Beach, Florida. She helped the George McGovern presidential campaign in October 1972 at Star-Spangled Women for McGovern–Shriver, reciting a parody of Erich Segal’s Love Story for 19,000 people at Madison Square Garden.

In 1973, Thomas joined Gloria Steinem, Patricia Carbine, and Letty Cottin Pogrebin as the founders of the Ms. Foundation for Women, the first women’s fund in the US. The organization was created to deliver funding and other resources to organizations that were presenting liberal women’s voices in communities nationwide.

In 1976, Thomas made a guest appearance on the NBC situation comedy The Practice as a stubborn patient of her father Danny Thomas’s character Dr. Jules Bedford, and the chemistry of father and daughter acting together made for touching hospital-room scenes.

In 1977 Thomas was a guest on Donahue, the television talk show, when she and host Phil Donahue fell in “love at first sight.” They were married on May 21, 1980 Thomas is stepmother to Donahue’s five children from his first marriage. Concerning her relationship with her stepchildren, Thomas told AARP in May 2012, “from the very first day, I decided that I was not going to try to be a ‘mother’ to Phil’s children in the traditional sense — they already had a mom — but, instead, to be their friend. I’m proud to say that the friendships I established with them are as strong today as they were 30 years ago — even stronger.”

In 1979, the Supersisters trading card set was produced and distributed; one of the cards featured Thomas’s name and picture.

After That Girl, eager to expand her horizons, Thomas attended the Actors Studio, where she studied with Lee Strasberg until his death in 1982, and subsequently with Strasberg’s disciple Sandra Seacat. When she won her Best Dramatic Actress Emmy in 1986 for the TV movie Nobody’s Child, she thanked both individuals.

In 1996, she was awarded the Women in Film Lucy Award in recognition of her excellence and innovation in her creative works that have enhanced the perception of women through the medium of television.

In 2010, Thomas created MarloThomas.com, a website for women aged 35+, associated with AOL and the Huffington Post.

Thomas’s Broadway theatre credits include Thieves (1974), Social Security (1986), and The Shadow Box (1994), and in 2011, she starred as Doreen in Elaine May’s comedy George Is Dead in Relatively Speaking during a set of three one-act plays (The New York Times called Thomas’ performance “sublime”). The other two plays were written by Woody Allen and Ethan Coen.

On November 20, 2014, the Marlo Thomas Center for Global Education and Collaboration was opened as part of St. Jude Children’s Research Hospital. Hillary Clinton presided over the ribbon-cutting ceremony.

On November 24, 2014, President Barack Obama awarded Thomas the Presidential Medal of Freedom, the highest honor an American civilian can receive, at a White House ceremony.

Off-Broadway, Thomas has appeared in The Guys, The Exonerated (in which she also appeared in Chicago and Boston, co-starring with Brian Dennehy), The Vagina Monologues and Love, Loss, and What I Wore. Also off-Broadway, she appeared opposite Greg Mullavey in the 2015 New York debut of Joe DiPietro’s play Clever Little Lies at the Westside Theatre. Regional theatre productions include: Who’s Afraid of Virginia Woolf? at the Hartford Stage; Woman In Mind at the Berkshire Theatre Festival; Paper Doll, with F. Murray Abraham at the Pittsburgh Public Theatre; and The Effect of Gamma Rays on Man-in-the-Moon Marigolds at the Cleveland Playhouse. In 1993, she toured in the national company of Six Degrees of Separation. In the spring of 2008, she starred in Arthur Laurents’s last play, New Year’s Eve with Keith Carradine, at the George Street Playhouse.