Janet Margolin was born on July 25, 1943, in New York City to a Jewish family. Her father, Benjamin Margolin, was a Russian Jewish accountant who founded the Nephrosis Foundation, now the Kidney Foundation of New York, and her mother, Annette (née Lief), was a dental assistant.

Growing up, she was surrounded by theater enthusiasts, and her father's friends often encouraged her to audition for roles. Initially aspiring to become a doctor, she eventually decided to pursue acting, influenced by her father's friends.

Janet Margolin attended the High School of Performing Arts and made her Broadway debut at the age of 18 in Morris West's "Daughter of Silence," where she earned a Tony nomination for her performance.

Her first movie role came in 1962 with "David and Lisa," where she played the female lead opposite Keir Dullea. This role garnered critical acclaim, but her career did not immediately take off as expected.

Throughout the 1960s, she appeared in several films, including "Morituri" with Marlon Brando and "Nevada Smith" with Steve McQueen. She also starred in "Enter Laughing" and "Take the Money and Run," directed by Woody Allen.

In 1977, she played the social-climbing wife in Woody Allen's "Annie Hall" and co-starred with Roy Scheider in the thriller "Last Embrace" in 1979.

Her last film appearance was in "Ghostbusters II" in 1989, and her final television roles were in "Murder, She Wrote" and "Columbo: Murder in Malibu" in 1990.

Janet Margolin was married twice. Her first marriage was to Jerry Brandt in 1968, which ended in divorce in 1971. She later married actor Ted Wass in 1979, and they had two children, Julian and Matilda.

Sadly, she was diagnosed with ovarian cancer and passed away on December 17, 1993, at the age of 50. She was cremated, and her ashes were placed in an urn garden at Westwood Memorial Park in Los Angeles.