(1995) and Ph.D (1996) from St John's College, Cambridge, and studied at the Cavendish Laboratory with John Rodenburg, before taking up post-doctoral research at Oak Ridge National Laboratory (ORNL) in Tennessee with ex-Cavendish researcher Stephen Pennycook.

He left academia for four years to work for another ex-Cambridge microscopy pioneer, Ondrej Krivanek, at Nion, his newly formed company in Seattle.

Nellist then returned to Trinity College Dublin and finally to the University of Oxford, where he became Joint Head of the Department of Materials in 2019.

[7][8] In 1998, working with Stephen Pennycook of ORNL, he recorded "the highest resolution microscope images ever made of crystal structures".

[9][10] Six years later, Nellist, Pennycook, and colleagues at ORNL produced the first images of atoms in a crystal on sub-Angstrom scales by using a new technique to correct the optical aberrations in a scanning transmission electron microscope.