Julietta was responsible for overseeing the NHS Breast Screening Programme in England until she left Public Health England in August 2015. She had first joined the NHS in 1979 and been involved in screening since the establishment of the Breast Screening Programme in 1987. In 1990 she was appointed National Coordinator of the Breast Screening Programme and gradually took on increased responsibilities.
She was appointed Visiting Professor in Cancer Screening at the University of Oxford in April 2008 following increasing involvement in research there and an honorary fellowship. Her chief research interest is as PI of the breast screening Age Extension trial which randomises about 500,000 women per year.