Sweeney played as a midfielder and began his career at Millwall where he progressed through their youth team and broke into the first team. He played in the 2004 FA Cup Final were Millwall lost 3–0 to Manchester United. He joined Stoke City in the summer of 2005 for a fee of £250,000 but his start at Stoke was hampered by injuries. He struggled to fully recover and after spending time out on loan at Yeovil Town and Walsall he joined Leeds United in January 2008. After a brief spell at Elland Road Sweeney played for Grimsby Town, Bury, AFC Wimbledon, Dartford and Greenwich Borough.