In 1954 she was cast in Rear Window. She did not even know who Hitchcock was and did not consider herself an Actress. Hitchcock had selected her based on a publicity photo of her wearing a black leotard and green feather boa. In Rear Window, she played one of the neighbors of protagonist L. B. Jeffries (Jimmy Stewart), a wheelchair-bound Photographer who passes the time spying on the other tenants of his apartment building. Her Nameless character, who was dubbed "Miss Torso", practiced her dance moves in a skimpy top and a pair of pink shorts with a 21-inch waistband, courtesy of famed costume designer Edith Head. She had no lines in the film until the end when she greets Stanley who has returned from military Service.

Hitchcock told Darcy that she should get an agent and that if she studied Anton Chekov in Europe, he could make her a movie star when she returned. She ignored both pieces of advice and thought he was joking about the latter. She was paid $350 for her work in Rear Window and had a sporadic acting career. Her most substantive role was in the Chubby Checker film Don't Knock the Twist (1962). She played Madge Albright, a "dancing firestorm" who is part of a brother-sister dance team. She also appeared in the films Women and Bloody Terror (1970) and The Delta Factor (1970).

Darcy was the subject of the 2004 documentary short film Remembering Miss Torso by Director Malcolm Venville.

She died of natural causes and was survived by her husband of thirty years, actor Byron Palmer. She was said to be the last surviving credited cast member of Rear Window. However, Frank Cady, who appeared as the Thorwalds' upstairs neighbor, survived until 2012 and Harry Landers, who played the uncredited role of Miss Lonelyheart's guest, died in 2017. Rand Harper, who played the role of the honeymooning groom, also survives.