Weld was born Susan Ker Weld in New York City. After her father died, her mother put her to work as a child model. Weld's first acting job was on television at age 12. She was in a movie the same year with a small role in the 1956 Alfred Hitchcock crime drama, "The Wrong Man". The pressures of her career, however, resulted in a nervous breakdown at age nine, alcoholism by age 12, and a suicide attempt around the same time.