Following costar John Ritter's death in 2003, DeWitt became the sole surviving cast member to have a starring role in all eight seasons of Three's Company.

After costar Suzanne Somers' death in 2023, DeWitt subsequently became the sole surviving cast member in a starring role to be present at the sitcom's onset.

Subsequently, while she was performing in summer stock, the director convinced her to enroll in UCLA's Department of Theater MFA program,[5] where she was awarded the Master of Fine Arts Fellowship as well as the Clifton Webb Scholarship.

[8] DeWitt is best known for her role as Janet Wood during the 1977–1984 run of the sitcom Three's Company, a job she obtained after being cast in the show's second pilot.

[9] In June 2011, DeWitt succeeded Eve Plumb in the title role of the play Miss Abigail's Guide to Dating, Mating & Marriage at the Downstairs Cabaret Theatre in New York City's Times Square.

[10] In 2012, DeWitt appeared in two separate stage productions of Love Letters starring opposite Tab Hunter and Tony Dow, respectively.

[14] DeWitt's appearance on Somers' program marked the first time the two actresses had seen or spoken to each other since having a major falling out 31 years earlier, involving a salary dispute.

[16] DeWitt participated with members of the House and Senate at the Capitol Hill Forum on Hunger and Homelessness, and has hosted presentations for the Family Assistance Program of Hollywood.