Thomas' parents, George and Mary (née Rowady) Thomas, immigrated to the U.S. from Tripoli, located in northern Lebanon. Her parents could neither read nor write, and her father's surname, which was "Antonious", was anglicized to "Thomas" at Ellis Island. She was born in Winchester, Kentucky, the seventh of nine children but was largely reared in Detroit, Michigan, where her family moved when she was four years old, and where her father ran a grocery store.

Thomas said "I was very lucky to be born in America.... [My family was] never hyphenated as Arab-Americans. We were American, and I have always rejected the hyphen and I believe all assimilated immigrants should not be designated ethnically." Of growing up in Detroit in the 1920s, she said, "They wanted to make you feel you weren't 'American'... We were called 'garlic eaters'". She was called "foreigner" in Detroit schools, leading to her coming home in tears.

She was raised as a Christian in the Greek Orthodox Church

Thomas attended Wayne University in Detroit,