After attending Talbot Heath School Ashcroft gained a degree in Natural Sciences, and then a PhD in zoology from Cambridge in 1978. Ashcroft then did post-doctoral research at the University of Leicester and the University of California at Los Angeles.
Ashcroft was elected a Fellow of the Royal Society in 1999. In 2007 Ashcroft was awarded the Walter B. Cannon Award, the highest honour bestowed by the American Physiological Society. She was one of five 2012 winners of the L'Oreal-UNESCO Award for Women in Science.
Ashcroft appeared (as a diner) on MasterChef during the 2011 series, along with several other Fellows of the Royal Society.
Ashcroft delivered the Croonian Lecture at the Royal Society in 2013.
In the 2015 Queen's Birthday Honours, she was appointed a Dame Commander of the Order of the British Empire (DBE) 'for services to Medical Science and the Public Understanding of Science'.