Stevens was educated at St Lawrence College, Ramsgate, and Leicester and Southampton Universities.
Stevens joined the Metropolitan Police in 1963. He subsequently served as Assistant Chief Constable, Hampshire Constabulary, Deputy Chief Constable, Cambridgeshire Constabulary and Chief Constable, Northumbria Police. He served as HM Inspector of Constabulary before rejoining the Metropolitan Police as Deputy Commissioner in 1998. He succeeded Sir Paul Condon as Commissioner in 1998. He was made a peer in 2005.
Directorships and interests
- Non-executive Chairman, Mercer Street Consulting Ltd
- Non-executive Director, Travelex (money exchange)
- Non-executive Chairman, Monitor Quest Limited (risk mitigation) Stevens was appointed a director of Quest Global in November 2005. 
- Non-executive Chairman, Protector Group (security services)
- Executive Chairman, Axiom International Ltd (forensic science and police training courses)
- Non-executive Director, LGC Limited (diagnostic services)
- Stevens Consultancy
- Contracted to JLA to give speeches on leadership, management and policing
- Member, UN Commission for Global Road Safety (funded by World Bank)
- Chairman, Buddi Ltd (GPS personal tracking device and tagging company)
- Senior Adviser to the Prime Minister on International Security
- Chairman, Border Security Advisory Committee (set up by David Cameron MP for Conservative Party) Since 1 January 2010 leading Stevens 3 Enquiry and examining certain cases investigated by Historical Enquiries Team, Northern Ireland
- Chairman, Independent Commission on the Future of Policing