Callan made her first TV appearance at the age of 20, playing a Western Union operator on an episode of Route 66 that happened to be shooting in Dallas. She did not resume her on-camera career until 1970, but worked steadily thereafter, having guest-starring roles on One Day at a Time, St. Elsewhere, Carnivàle, JAG, Coach and King of the Hill. She played a key role in the Emmy Award-winning episode "Cousin Liz" of All in the Family and portrayed the mother of April Stevens Ewing in several episodes of the penultimate season of Dallas. She played Daisy LaRue in the TV show Meet the Browns and appeared as Gabe Duncan's teacher, Mrs. Monroe, in Good Luck Charlie. She also appeared in the third season finale of Desperate Housewives as Ilene Britt, the mother of Edie Britt, and has portrayed Lily's maternal grandmother on several episodes of How I Met Your Mother. She played the part of Charlie in Heroes for one episode.
She appeared in the films Joe (1970), The Onion Field (1979), Fast-Walking (1982), and A Change of Seasons (1980) and the television adaptation of the Lanford Wilson play The Rimers of Eldritch.