Pewsey attended Southend High School for Boys and was a founder member of Southend Action Group for the Arts. He was later a founder member of the Beckton Residents Association, serving as its first Secretary, and has been Secretary of the Loughton Residents Association since 2007. He began his writing career in the 1970s contributing to local magazines. In 1990 he established the Essex Calf  group of local historians, a prolific group of writers who have had over 50 books and booklets published, together with several hundred articles, maps, videos, DVDs and contributions to broadcast media. Members of the group have also organised local history exhibitions, walks, tours and special events, and are active in the public realm on heritage issues.
He has served in various capacities on numerous heritage bodies, including the British Association for Local History (Publications Committee), Essex Archaeological & Historical Congress (Secretary 1996-99, Chairman 2008-2011, President 2011-date), Essex Society for Archaeology & History, Loughton & District Historical Society, Newham History Society, and Wanstead Historical Society. He was Deputy Mayor of Loughton 2011-12 and Mayor in 2012-13, having also served on Loughton Town Council as Chairman of its Resources & General Services Committee and its Environmment & Heritage Committee. He founded the Loughton Film Society in 2010, and was its first Chairman, and in 2014 was the organiser of the first Loughton Art Trail. He is also a committee member of the Loughton Festival, and is Vice-Chairman of the Lopping Endowment, a charitable trust which manages Lopping Hall, a community arts venue, in Loughton. He has acted as historical consultant for a wide range of heritage projects in Essex and East London.
The Essex Calf group takes its name from the traditional nickname given to Essex folk; in the later Middle Ages, Essex was best known to the outside world for the huge quantity of excellent beef calves sent from Essex to the London meat markets, so ‘Essex Calf’ became a slang term for anyone from the county. Stephen Pewsey’s specialisms within the group include the history of Epping Forest, Newham, South-east Essex, and Essex’s historical links with the United States of America.
-  Stratford: A Pictorial History, and Epping & Ongar: A Pictorial History
-  Images of England: Chingford
- Works by or about Stephen Pewsey in libraries (WorldCat catalog)