From 2003 to 2006, Johnston was co-ordinator of the Oxford Access Scheme. He then became a director of Future, holding his role from 2006 to 2009. Before standing for election, he was chief executive of the Social Mobility Foundation for over ten years, from 2009 to 2020. He worked alongside his partner Charlotte Pickles during this time and they received tickets from the UK government to attend the opening ceremony of the
2012 Olympic Games together. He was also a member of the
Social Mobility Commission from 2012 to 2017. Johnston was a governor at Sir George Monoux Sixth Form College, where he had studied, from 2008 to 2016, as well as
Pimlico Academy from 2008 to 2017. == Parliamentary career==