Fletcher had a recurring role as the Bajoran religious leader Kai Winn Adami in the television series Star Trek: Deep Space Nine (1993–1999).

)[9] Also in 1959, she appeared in an episode of the original Untouchables TV series starring Robert Stack, "Ma Barker and Her Boys", as Elouise.

In the summer of 1960, she was cast as Roberta McConnell in the episode "The Bounty Hunter" of Tate, starring David McLean.

In 1974, Fletcher returned to film in the crime drama Thieves Like Us, co-produced by her husband Jerry Bick and Robert Altman, who also directed.

Meanwhile, director Miloš Forman saw Fletcher in Thieves and cast her as McMurphy's nemesis Nurse Ratched in One Flew Over the Cuckoo's Nest (1975).

Fletcher's film roles were in such features as Exorcist II: The Heretic (1977), The Cheap Detective (1978), The Lady in Red (1979), The Magician of Lublin (1979), Brainstorm (1983), Firestarter (1984), Invaders From Mars (1986), Flowers in the Attic (1987), Two Moon Junction (1988), Best of the Best (1989), Blue Steel (1990), Virtuosity (1995), High School High (1996), and Cruel Intentions (1999), as the aunt of Ryan Phillippe's Sebastian.

Additionally, she played the character Ruth Shorter, a supporting role, in Aurora Borealis (2005), alongside Joshua Jackson and Donald Sutherland, and appeared in the Fox Faith film The Last Sin Eater (2007).

From 1993 to 1999, she held a recurring role in Star Trek: Deep Space Nine as the scheming Bajoran religious leader Kai Winn Adami.