Stewart is a Chartered Accountant. He was the founder and Chairman of Newton Investment Management from 1977-2002. He is President of Veritas Investment Partners Ltd, the holding company of Veritas Investment Management LLP, and a Board member of VenCap (Channel Islands) Ltd. Stewart was a Non-Executive Director of HSBC Holdings plc from 2002-2008, a Council Member of Imperial College and the Chairman of the committee advising the Council on the Endowment Fund from 2007 to 2015 and a Director of The Herald Investment Trust plc from 2012 to 2015. He formerly sat on the Investment Committee of The Wellcome Trust and Investment Board of Cambridge University. Stewart is an active investor in private healthcare and technology companies in the UK.