Accra Hearts of Oak SC
He began his football career in 2001 with Fauzan F.C. before he moved to Liberty Professionals FC. Where he was made the captain of the team. In December 2008 Mumuni left his club Liberty Professionals FC on loan to Bendel Insurance F.C., after his return in October 2009 he signed for Accra Hearts of Oak SC. The 2008 league champions and the most successful club in Ghanaian top league on 7 October 2009 he signed a new contract with them. Best defender Ghana Premier League 2007/2008. Most disciplined player 2008/2009 League season.