From 1986 to 1995, Vallance taught at St George's Hospital Medical School, where his research concentrated on vascular biology and endothelial cell physiology.

[2] In addition to Collier, he has been inspired by physician Tom Pilkington and former Regius Professor of Physic at Cambridge Sir Keith Peters.

[9] Prior to taking up senior positions with the pharmaceutical company GlaxoSmithKline (GSK) and later in the UK Government, Vallance spent several years in medical research.

[11] From 1986 to 1995 Vallance taught at St George's Hospital Medical School,[2][10] where his research concentrated on vascular biology and endothelial cell physiology.

Furchgott and Zawadzki subsequently showed that the occurrence was mediated by what they called endothelium-derived relaxing factor, later found to be nitric oxide, and it was shortly shown to occur in a variety of animals.

[1][15] Subsequently, their team showed that the human arterial vasculature is actively dilated by a continuous release of nitric oxide.

He championed open innovation and novel industry-academic partnerships globally,[13][31][29] and maintained a focus on the search for new antibiotics and treatments for tropical diseases.

[13][32] In March 2018, Vallance left GSK, and on 4 April 2018 he began his five-year tenure as Chief Scientific Adviser to the UK Government, replacing the interim officeholder Chris Whitty.

[38] In September, it emerged that Vallance owned a deferred bonus of 43,111 shares worth £600,000 in GlaxoSmithKline, a company which was working on developing a COVID vaccine.

The GCSA has no input into contractual and commercial decisions on vaccine procurement which are taken by Ministers following a robust cross-Government approvals regime".

[41] After a televised briefing alongside Johnson and Whitty on 31 October, where a second "lockdown" was introduced for England, Vallance was criticised for showing two slides – projecting hospital admissions and deaths – which were later reissued with worst-case figures revised downward.

[2] The following year he delivered the Goulstonian Lecture of the Royal College of Physicians, where he gave details of the connection between nitric oxide and blood pressure.