Roc began as a stage actress, debuting in the 1938 London production of Nuts in May, in which she was seen by Alexander Korda who cast her in a leading role as a Polish princess in The Rebel Son.She was employed by the studio of J. Arthur Rank, who called her "the archetypal British beauty" She achieved her greatest level of popularity in British films during the Second World War in escapist melodramas for Gainsborough Studios.She played prominent roles in some patriotic films of the period, such as Let the People Sing (1941) with Alastair Sim and We'll Meet Again (1943) with Vera Lynn. She co-starred with Phyllis Calvert, Jean Kent and Flora Robson as an internment camp inmate in Two Thousand Women (1944).Love Story (1944) allowed her to play the jealous rival of Margaret Lockwood. She later commented that although they were required to slap each other's faces, she and Lockwood were always the best of friends. They played rivals in two subsequent films, The Wicked Lady (1944) and Jassy (1945). Roc's more overt sexuality in such films as The Wicked Lady was downplayed for the American market; her décolletage led US censors to call for retakes to de-emphasise it) and "the Goddess of Odeons", whilst Noël Coward said she was "a phenomenon" and "an unspoiled movie star who can act". She played the central role in Millions Like Us, a powerful World War Two film, made by Launder and Gilliat, which portrayed the changes that wartime wrought on the 'home front', starring alongside Gordon Jackson.Her brief move to Hollywood to film Canyon Passage (1946) was a lend lease agreement between Rank Pictures and Universal Studios of British in return for American film actors. During filming, Roc was romantically linked with Ronald Reagan, while her US co-star Susan Hayward stated "that Limey glamour girl is a helluva dame."Roc returned to England later in the decade following the death of husband André Thomas. She produced only 3 more films and made a few television appearances (including the first episode of The Saint).