Blair's paternal grandparents were Jewish immigrants (from Poland and Russia), and her maternal grandfather was from a Jewish family from Ukraine/Russia. Her maternal grandmother was of Scottish (from Lanarkshire) and English (from Warwickshire) ancestry.
Selma Blair Beitner was born on June 23, 1972, in Southfield, in the metropolitan area of Detroit, Michigan, the United States. She is the youngest of four girls. Her sisters are Katherine, Elizabeth, and Marie Beitner.
Blair had a Jewish upbringing; her Hebrew name is Bat-Sheva. When she was 23, her parents, Elliot and Molly Ann Beitner divorced, and the actress legally dropped her father's last name, Beitner. Her mother was a judge, while her father was an attorney and an active member of the United States Democratic Party.