Ursula was born in 1924 to Wilhelmine Lange and Hans Schmidt. At age 17, for refusing to join the Hitler Youth, she was drafted into Service working as farm labor. After that, she returned to do acting on stage, where she met and married her first husband, German film Producer Georg Otto Thiess. They had two children, Manuela and Michael. That marriage dissolved in 1947, and in 1948, she began a modeling career in Berlin. Her unusual beauty caught the eye of Howard Hughes, who made her a contract offer to join RKO Studios.

She met Robert Taylor in 1952 and they married on May 23, 1954 in Jackson Hole, Wyoming. She virtually abandoned her film career to become a mother and housewife. The Taylors had two children Terrance "Terry" (b. June 18, 1955 in Santa Monica, California) and Tessa (b. August 16, 1959 in Santa Monica). They moved with Ursula's two children from her previous marriage, to their 114-acre (0.46 km) ranch in Brentwood, California, in 1956, and lived there until Taylor's death from cancer in 1969. Ursula's two children, Manuela and Michael, had many adjustment problems adapting to their new life, and were often in trouble with the police, causing the family to suffer bad publicity as a result. Her son, Michael, who had served a year in a German prison for attempting to poison his natural father, died of a drug overdose on May 26, 1969, shortly before Robert Taylor's own death. Ursula discovered him dead when she stopped by his motel to drop off some medication for him.

After Taylor's death, she was obliged to sell their ranch. She moved to Bel Air, and in 1973, she married film distributor Marshall Schacker. They remained married until his death from cancer in 1986.

Thiess died of natural causes in an assisted living care facility in Burbank on June 19, 2010, at the age of 86. She was survived by three of her four children, Manuela, Terry, and Tessa. She is interred alongside her husband and her son at Forest Lawn Memorial Park (Glendale).