Young was born on January 25, 1945, in Washington, D.C. She added the surname Taylor, which was the surname of her stepfather, a Detroit executive. Her father was a diplomat, and her younger siblings are actress/sculptor Dey Young and writer/director/producer Lance Young. The siblings were raised in Oakland County, Michigan. Leigh graduated from Groves High School, Beverly Hills, Michigan in 1962. Before attending Northwestern University as an economics major, she spent a summer shifting scenery, modelling, acting, and sweeping up at a Detroit little theater. However, she left Northwestern before graduating to pursue a full-time acting career, making her professional debut on Broadway in Three Bags Full. About dropping out of college, the Actress explained:

Taylor-Young got her first big break in 1966, when she was cast as Rachel Welles on the primetime soap opera Peyton Place. Her character was written in the show as a replacement for the character of Allison MacKenzie, previously played by Mia Farrow. The series' Producer, Everett Chambers, cast her because of her "great warmth and sweet Angelic qualities not unlike Mia". At the time she received the role, Taylor-Young had been in California for only a few days. She initially went there in April 1966 to recuperate from an attack of pneumonia. She impressed the head Producer of Peyton Place, Paul Monash, with a performance from The Glass Menagerie and was immediately signed to a seven-year television and multiple motion picture contract.

Leigh Taylor-Young married Ryan O'Neal, her Peyton Place co-star, in 1967. Their wedding was a spontaneous one: while in Hawaii for a promotion for Peyton Place, an ABC manager offered the couple the opportunity to marry at his home. The marriage produced a son, Patrick, but Leigh and O'Neal divorced in 1973.

For the next several years, her pictures tended to be high budget films, such as The Adventurers (1970), based on the novel by best-seller Harold Robbins, and The Horsemen, (1971) opposite leading man Omar Sharif. She is perhaps best known for her performance as Shirl, the "furniture" girl, in the science fiction classic Soylent Green (1973).

She lived in India for almost two years and returned to the United States in 1976. Her sister is Actress Dey Young, who also appeared on Star Trek; and her brother is Director Lance Young, who directed the movie Bliss. Leigh wed Director Guy McElwaine in 1978 and they later divorced.

The 1980s saw Leigh Taylor-Young return to both film and television, where her looks and voice often led to casting in roles of an aristocratic bent. In 1981, she appeared in the high Technology Michael Crichton production Looker. In 1985, she was cast as Virginia Howell in Jagged Edge, and appeared in the romantic comedy Secret Admirer.

In addition to her film work, she guest-starred on such television series as McCloud, Fantasy Island, The Love Boat, Hart to Hart, Hotel and Spenser: For Hire. She returned to her soap opera roots in 1983, appearing in the short-lived primetime series The Hamptons. From 1987-89, she played Kimberly Cryder, a recurring character on Dallas, her first role in a major prime time soap since Peyton Place.

Despite being best known for her film and television work, she has stated a preference for live theater where her career began. A favorite of Samuel Beckett, she starred opposite Donald Davis in Beckett's one act play, Catastrophe (included in a trilogy of one-act plays billed as The Beckett Plays) at the Edinburgh International Festival in 1984. Catastrophe with Taylor-Young also toured Los Angeles, New York City and London.

Taylor-Young's recent film credits have included minor roles in Honeymoon Academy (1990), Bliss (1997), and Slackers (2002), as well as direct-to-video films Addams Family Reunion (1998), Klepto (2003), Spiritual Warriors (2007) and The Wayshower (2011).

Perhaps her best-known television work was on the CBS series Picket Fences, in which she played mercurial and cougarish mayor Rachel Harris from 1993 through 1995. She won an Emmy Award for the role in 1994, for Outstanding Supporting Actress in a Drama Series, as well as a Golden Globe nomination the following year. From 2004 through 2007, she played Katherine Barrett Crane on the soap opera Passions.

She married John Morton in January 2013 at PRANA, headquarters of the Movement of Spiritual Inner Awareness in Los Angeles. She is an ordained minister in the Movement of Spiritual Inner Awareness, founded by the late John-Roger Hinkins and now led by her husband..