Thomas was born to Gladdy Lou Ryder, who was a special education teacher in the Santa Monica-Malibu Unified School District. Thomas graduated from Santa Monica High School in 1975 and went on to attend UCLA Film School, graduating in 1980. While at UCLA, she was a member of the Chi Omega sorority and was romantically linked with then unknown actor Corbin Bernsen. She overcame a cocaine addiction in the 1980s. Thomas married entertaiment attorney Skip Brittenham in October, 1992. Their daughter, India Rose, was born on June 19, 2000.