Justin trained as a biologist at the University of York, UK and went on to study the molecular mechanism of muscle contraction for his PhD. He held a NATO post-doctoral fellowship at the University of Vermont, working on the mechanical properties of insect flight muscle.
He then returned to the University of York where together with David White he developed optical tweezers to measure the force and movement produced by a single myosin molecule. He obtained a Royal Society University Research Fellowship and his new lab developed single molecule methods in order to study how biological molecules work both in vitro and within living cells.
Justin later moved to the MRC National Institute for Medical Research and joined the Francis Crick Institute in 2015. His research team use single molecule techniques; including optical and magnetic tweezers, TIRF microscopy and atomic force microscopy to help increase our understanding of energy transduction by biological macromolecules.
He is also Chair of the Board of Trustees for the National DeafBlind charity SENSE.