She was born Sara Viola Warmbrodt in Arkansas City, Kansas, the daughter of Samuel Sylvester Warmbrodt (October 8, 1861 – January 6, 1948) and Elizabeth Ann (née Wilson; February 10, 1864 – February 7, 1932). Her paternal grandfather was from Switzerland.
Sothern was a seasoned actress by the time she made her Broadway debut in The Dagger (1925). That was followed by Arabesque and Fool's Bellsthat same year. She next appeared in Mama Loves Papa (1926). During that time, she acted in plays across the country, including the theatre venues of Downtown Los Angeles. She married art dealer Francis Lenn Taylor in 1926 in New York City. They were the parents of Howard Taylor (born 1929) and the movie star Elizabeth Taylor (1932–2011).
After her marriage, Sothern retired from the stage and never acted again. After living in England several years, where her children were born, they returned to the United States. Living in Los Angeles, California, she devoted herself to her family and the movie career of her daughter. Sothern died at age 99 in Palm Springs. She is interred beside her husband in Westwood Village Memorial Park Cemetery, Westwood, California