Ulric was discovered by theatrical producer David Belasco who first saw her in The Bird of Paradise in 1913, after Ulric wrote to him requesting that he see her on stage. Belasco, who would go on "fishing trips" to find new stage talents, recalled that it was often a long time between "bites," but he enjoyed the sport as he sometimes would "hook a big one."
After watching her on stage, he asked her to audition at his playhouse. He watched her perform while he sat incognito in one of the theater's seats. "After twenty minutes," he said, "I knew I was watching a very talented and unusual young woman." He then offered her the leading role in The Heart of Wetona. He recalled: "Among the biggest I have ever landed is, I believe, little Miss Ulric: I think she will grow bigger every season she is before the public."
Under Belasco's management during most of her stage career, Ulric played a variety of female roles. Among them was her portrayal of Rose, a French-Canadian orphan, in Tiger Rose (1917).
Biographer William Winter called her a "born actress," someone who Belasco hoped would fulfill the theater's need for talent. Winter also notes that no one in her family had ever been involved in acting, adding: "She resorted to the dramatic calling not through mere vanity, the impulse of personal exhibition, or the acquisitive hope of profit, but because her natural vocation is acting." Lenore came to Hollywood in 1929 and appeared in Frozen Justice and South Sea Rose. She signed with Fox Film Corporation to make several films with an approximate salary of $650,000. Frozen Justice was directed by Allan Dwan. Some of the scenes were filmed in Alaska. She was successful in a supporting role in Camille, starring Greta Garbo. Ulric returned to Broadway in 1940, acting in The Fifth Column by Ernest Hemingway and again in 1947, in a revival of Antony and Cleopatra.