Prior to running for the House, Mustio was a partner in an insurance brokerage firm.
In 2000, Mustio was elected to the Moon Township Board of Supervisors, serving as chairman of that body.
For the 2009-10 legislative session, Mustio serves on the House Labor Relations, Liquor Control, Professional Licensure and Urban Affairs Committees.
He is also a member of the Legislative Budget and Finance Committee, Pittsburgh Port Commission and the Joint State Government Commission Tasks Forces and Advisory Committee.
In 2012, Mustio ran for the Pennsylvania State Senate seat representing the 37th District to succeed retiring Republican incumbent John Pippy.