Cummins’ London stage debut was in the role of Maryann, the juvenile lead in Let’s Pretend, a children’s revue that opened at the St James’s Theatre on her 13th birthday.

[3] Her first major film was English Without Tears (1944) with Michael Wilding and Lilli Palmer, directed by Harold French and released in the United States as Her Man Gilbey.

[7][5] He tried her in two films directed by Joseph L. Mankiewicz, The Late George Apley (1947), playing the daughter of Ronald Colman, and Escape (1948), co starring with Rex Harrison.

Cummins returned to England to appear in That Dangerous Age (1948) for Alexander Korda, directed by Gregory Ratoff) with Myrna Loy and Roger Livesey.

She later starred alongside Dana Andrews in the horror film Night of the Demon (1957), directed by Jacques Tourneur,[5] and Hell Drivers (also 1957),[5] which featured Stanley Baker, Patrick McGoohan, and Herbert Lom.

In 1998, Gun Crazy (1950) was selected for preservation in the United States National Film Registry by the Library of Congress, as being "culturally, historically, or aesthetically significant."

Michael Adams wrote in Movieline in August 2009 that the film was "directed by B-movie specialist Joseph H. Lewis from a script co-written by MacKinlay Kantor and blacklisted Dalton Trumbo, "fronted" by his friend Millard Kaufman.

[citation needed] On 14 June 2006, she appeared as guest of honour at a special screening of Night of the Demon in Borehamwood, Hertfordshire, hosted by the Elstree Film and Television Heritage Group.

[11] On 29 September 2010, Cummins introduced the film Street Corner (1953) as part of the Capital Tales Event at BFI Southbank London hosted by Curator Jo Botting.

The screening location features prominently in the film, with shots of the courtyard before a key scene in which the psychologist Holden meets occultist Karswell for the first time in the British Library, which until 1998 was housed within the museum.

During the 1970s, Cummins was active in a national charity, Stars Organisation for Spastics, raising money and chairing the management committee of a holiday centre for children with disabilities in Sussex.

Cummins was a trustee of the charity which is run entirely by volunteers and raises funds for communication and mobility aids for people with cerebral palsy.

On 25 January 2013, Cummins was honoured at the Noir City Film Festival at the Castro Theatre in San Francisco with a screening of a restored print of Gun Crazy.