After guest-starring on various television series, including "Schlitz Playhouse of Stars", "The Gale Storm Show", "Sugarfoot", and "Markham", Lynn won the role of Thelma Lou on "The Andy Griffith Show". Despite playing the role for five years (1961–66), she appeared in only 26 episodes, and was never signed on to the show (in part because at the time she was cast, she was still under contract for "Texas John Slaughter"). She recounted, "I didn't want to leave Thelma Lou. I really loved her. I enjoyed her. She was sweet and kind, she was so fun to play, and I loved working with Don Knotts - he was so wonderful." Following the end of "The Andy Griffith Show", Lynn continued appearing in various television and film roles.