Professor Stephens graduated from Edinburgh University with a BSc (Hons) in Ecological Science. He was awarded an MSc in Soil and Water Engineering from Cranfield Institute of Technology in 1978 and later, a PhD on the effects of climate on the yield of tea in East Africa in 1992.
He began his career in environmental consultancy before undertaking irrigation research for the Malawi Government until 1984. He then joined Cranfield as a Research Officer working the agro-climatology of tea before joining the academic staff in 1990 as Lecturer and then Senior Lecturer.
In 1999, Professor Stephens was appointed Head of the newly founded Institute of Water and Environment at Cranfield’s Silsoe campus. From 2005, Professor Stephens became Change Programme Director, reporting to the Vice-Chancellor on the major developments on the Cranfield campus to accommodate the move of academic activities from Silsoe and the formation of the School of Applied Sciences and Cranfield Health. He led the development of Cranfield's Carbon Management Plan and currently chairs the University's Board for Energy and Environment.
Professor Stephens was the Cranfield University Nominated Trustee on the Bedford Charity from 2001 - 11. He was also a Commonwealth Scholarships Commissioner from 2004 to 2010. He is currently Director of the Marston Vale Trust, with which Cranfield has been involved since its inception.