Warren was born on June 22, 1949, in Oklahoma City, Oklahoma, as the fourth child of middle class parents Pauline (nee Reed, 1912–1995) and Donald Jones Herring (1911–1997). Her great-grandfather, John Hayne Herring, was an English immigrant who arrived in America in 1866. Warren has described her family as teetering "on the ragged edge of the middle class" and "kind of hanging on at the edges by our fingernails". She had three older brothers and was raised as a Methodist.
Warren lived in Norman until she was 11 years old, when the family moved to Oklahoma City. When she was 12, her father, a salesman at Montgomery Ward, had a heart attack, which led to many medical bills as well as a pay cut because he could not do his previous work. Eventually, their car was repossessed because they failed to make loan payments. To help the family finances, her mother found work in the catalog order department at Sears. When she was 13, Warren started waiting tables at her aunt's restaurant.
Warren became a star member of the debate team at Northwest Classen High School and won the state high school debating championship. She also won a debate scholarship to George Washington University at the age of 16. She initially aspired to be a teacher, but left GWU after two years to marry Jim Warren, whom she met in high school.
Warren and her husband moved to Houston, where he was employed by IBM, which was a subcontractor to NASA. She enrolled in the University of Houston and graduated in 1970 with a Bachelor of Science degree in speech pathology and audiology. For a year, she taught children with disabilities who were enrolled in a public school. Her qualifications were based on an "emergency certificate", because she had not taken the education courses that were required for a regular teaching certificate.
The Warrens moved to New Jersey when Jim received a job transfer. She soon became pregnant and decided to remain at home to care for their child. After their daughter turned two, Warren enrolled at the Rutgers University, Newark School of Law. She worked as a summer associate at Cadwalader, Wickersham & Taft. Shortly before graduating in 1976, Warren became pregnant with their second child. After she received her J.D. and passed the bar examination, she decided to perform legal services from home. She wrote wills and did real estate closings.
The couple had two children, Amelia and Alexander, before they divorced in 1978. Two years later, Warren married Bruce H. Mann, a law professor, but she decided to retain the surname of her first husband. She also has grandchildren.