[5] Among St Mary's founders was the surgeon Isaac Baker Brown, a controversial figure who performed numerous clitoridectomies at the London Surgical Home, his hospital for women, and who "immediately set to work to remove the clitoris whenever he had the opportunity of doing so.

[16] In the 1950s, Felix Eastcott, a consultant surgeon and deputy director of the surgical unit at St Mary's Hospital, carried out pioneering work on carotid endarterectomy designed to reduce the risk of stroke.

[5] In 1987 as part of on-going rationalisation within the NHS, the hundred year old Paddington Green Children's Hospital was closed down, the listed buildings sold off and its services absorbed into St Mary's.

In celebration of the association, a British Rail Class 43 (InterCity 125) locomotive, 43142, was named St Mary's Hospital, Paddington on 4 November 1986.

The charity funds a range of specialist equipment for the units, including ventilators and patient monitoring systems for those being treated on the wards,[29] as well as providing practical and emotional support to families.