She was a consultant surgeon at St Mary's Hospital in Paddington, central London, from 1982 to 2002, and in 1993 she became the first British woman to be appointed a professor of surgery.

Her mother suffered deep vein thrombosis and a pulmonary embolism during her difficult birth, which later influenced Mansfield's specialism in her medical career.

[1][3] She remained at St Mary's for the rest of her career, while also serving as an honorary consultant in paediatric and vascular surgery at Great Ormond Street Hospital.

[4] She was made a Fellow of the Royal College of Physicians in 2005, and was elected president of the British Medical Association in 2009–2010.

[5] Mansfield was appointed Dame Commander of the Order of the British Empire (DBE) in the 2023 Birthday Honours for services to surgery and equality in medicine.