Peacock was an original member of IMechE and co-founder of Beyer, Peacock and Company, the renowned locomotive manufacturers. Peacock was a precocious locomotive superintendent on the Leeds and Selby Railway, the line was acquired by the York and North Midland Railway in 1840 and he briefly worked under Daniel Gooch. In 1841, he became the Locomotive Superintendent of the Sheffield, Ashton-under-Lyne and Manchester Railway, subsequently the Manchester, Sheffield and Lincolnshire Railway. In this role he was responsible for founding the Gorton locomotive works for this railway, he left to form the partnership with Beyer.
From 1885-1889 he was Member of Parliament, Liberal Party Gorton division of Lancashire.