[1] Mossfield was born in Annandale,[1] but spent the majority of his life in Blacktown where he married and raised 8 children.
[3] Mossfield contested the 1996 federal election as Labor's candidate for the division of Greenway after the retirement of Russ Gorman.
Mossfield was returned at the 1998 federal election with a two party preferred vote of 59.94%, a swing of +6.55%.
While in parliament, Mossfield was deputy chair of the House of Representatives Standing Committee on Procedure, and was a member of the committees on: Employment, Education and Training; Environment, Recreation and the Arts; Legal and Constitutional Affairs; Communications, Transport and the Arts; Ageing, and Transport and Regional Services.
[2] On 21 April 2021, Mossfield was awarded a Key to the City of Blacktown, by mayor Tony Bleasdale.