Mark James Duffy (born 7 October 1985) is an English professional footballer who plays as an attacking midfielder or right winger for Tranmere Rovers.
Duffy began his career with the academies at Liverpool and Wrexham before joining non-league side Vauxhall Motors. From there he went to Prescot Cables and Southport and entered the Football League with Morecambe. He joined Scunthorpe United in January 2011, where he spent two-and-a-half years at Glanford Park and the 2013–14 season at Doncaster Rovers.
Duffy moved to Birmingham City in June 2014 but failed to establish himself in the side and was loaned out to Chesterfield and Burton Albion with whom he helped win promotion to the Championship. Duffy signed for Sheffield United in June 2016 and under the management of Chris Wilder the Blades won promotion from League One in 2016–17 and the Championship in 2018–19. In August 2019 Duffy joined Stoke City on loan for the first half of the 2019–20 season and then Dutch side ADO Den Haag in January 2020.