Her older sisters were Dr. Helen Seegar Stone (1895–1976), an educator; Dorothy Seegar (1897–1999), Actress and singer; Mildred (1905–1913), and Miriam Seegar (1907–2011), also an Actress. Following school, Seegar performed on stage in London, starting her career with Three Men on a Horse. She continued performing in London until the start of World War II, at which point she returned to the United States.

Starting in 1940, Seegar performed in Broadway plays, in film, on radio and on television. She played Elsie on Room for One More, was a regular on The Red Buttons Show and appeared as a character actor on television throughout the 1950s and 1960s, with roles on Suspense, Perry Mason, and The Donna Reed Show. She played ten different small roles on Bewitched over the course of that same series.

Sara Seegar met Ezra Stone while the two were performing in Horse Fever on Broadway in 1940. They were married on October 5, 1942. They had two children: a son, Josef Seegar Stone (1944–2010) and a daughter, Francine Lida Stone.

In the 1962–63 season of Dennis the Menace, Seegar played Eloise Wilson, the wife of John Wilson. She effectively replaced Sylvia Field, who portrayed Martha Wilson—the original "Mrs. Wilson"—from 1959 to 1962. Field left the series after the death of Joseph Kearns (George Wilson), due to George and Martha Wilson being written out of the series. John Wilson (Gale Gordon) began playing John Wilson, George's brother, after Kearns' death.

Sara Seegar Stone died on August 12, 1990, of a cerebral hemorrhage at St. Mary's Hospital, Langhorne, Pennsylvania; her ashes were scattered on nearby Stone Meadows Farm.