Dr Marshall is a biotechnologist and chemical engineer with a career spanning a range of primary industries including dairy, fruit, arable, meat and seafood. Previous roles include managing director of ViaLactia Biosciences Ltd, group director R&D of the New Zealand Dairy Board and chief executive of the New Zealand Dairy Research Institute (now Fonterra Research Centre).

Dr Marshall currently serves on a number of boards and committees, including Riddet CoRE (chair),  Food Industry Enabling Technologies (chair), Industry Advisory Panel for the High Value Nutrition National Science Challenge (chair), Bioresource Processing Alliance, Seafood Innovations Ltd and the Foundation for Arable Research Strategic Research Committee. He is a past member of the Investment Advisory Panel of the Primary Growth Partnership and the board of Plant and Food Research Ltd.  He is a reviewer for MBIE and Callaghan Institute projects.  A Fellow of the New Zealand Institute of Chemistry and a Fellow of the New Zealand Institute of Food Science and Technology (NZIFST), he was awarded the NZIFST JC Andrews Award for Distinction in Food Science and Technology in 2006 and the Distinguished Service Award in 2012.  He is an Honorary Member of the International Dairy Federation (IDF), past President of the Coordination Committee and Vice Chairman of the Codex Milk Committee.  In 2016 he was awarded the IDF Award, which recognises remarkable contributions to progress in dairying worldwide.