Born in Bedlington, Northumberland, Trewick started his career at West Bromwich Albion and played nearly 100 league games for the club during the late 1970s.
During West Brom's visit to China in 1978 he entered football history by, in reply to a question about the Great Wall, remarking "Impressive, isn't it?
His time at Newcastle was somewhat affected by injury, although he enjoyed a successful loan spell at Oxford United, whom he later joined on a free transfer in 1984.
The club remained in the lower reaches of the division, with their lowest ever Football League gate of 1,266 on 23 February at home to Northampton.
On 8 March 2010, Trewick was sacked, with chairman and former manager Graham Turner taking the job on a temporary basis.