Mary Ann Stewart, the widow of U.S. Supreme Court Justice Potter Stewart, died March 4 at an assisted-living center in Brattleboro, Vt. She was 93.

She had pneumonia, said her daughter, Harriet Stewart Virkstis.

Mary Ann Bertles — she was known for much of her life as “Andy” — was born June 3, 1919, in Grand Rapids, Mich. She grew up in New York and in Bermuda, where her father, an investment banker, had built a home.

She studied child psychology at Bennington College in Vermont before working as a researcher and photographer for Life magazine in New York City, where she met her future husband, her daughter said. The Stewarts were married in 1943.

Known on the bench as a crucial swing vote, Potter Stewart served on the Supreme Court from 1958 to 1981. He died in 1985.

Mrs. Stewart resided in the District until 2008, when she moved to Vermont. She did philanthropic and volunteer work with UNICEF, the National Osteoporosis Foundation, the Jefferson Awards for public service, and organizations devoted to family services and juvenile justice, her daughter said.

Survivors include three children, Harriet Stewart Virkstis and Potter Stewart Jr., both of Brattleboro, and David B. Stewart of Chatham, Mass.; a sister; nine grandchildren; and three great-grandchildren.