Ten years later, he became 2nd Deputy Mayor in Schaerbeek and finally mayor in 2001.
In June 1989, he was elected to the Brussels Parliament and was reelected in 1995, 1999 and 2004.
He has held different posts such as Vice-president of the Brussels Regional Council and President of the Committee for Town and Country Planning and Land Policy.
In 2007, Clerfayt was elected to the Belgian Chamber of Representatives and was appointed in 2008 as the Secretary of State for Finance in charge of the modernisation of the Department of Finance, green taxation and the fight against tax fraud.
In 2010 he was re-elected to the federal chamber.
Clerfayt was re-elected mayor of Schaerbeek in 2012 at the head of a governing coalition of his own party with Ecolo (green party) and the CdH (Christian-democrats).