Sternhell began his career as a research chemist in private industry with Monsanto in 1953. Two years later, he was appointed a senior research officer at CSIRO and remained in that position until 1964. Sternhell was a senior lecturer in the Department of Organic Chemistry at the University of Sydney, from 1964 until 1967. He spent a further ten years as a reader in organic chemistry at the University of Sydney before being appointed Professor of Organic Chemistry. He was an Emeritus Professor from 1999. In 1991–92, he was chairman of the Australian Research Council Chemical Sciences Panel.