McMullan became Manager of Opposition Business (opposite number to the Leader of the House) in 1998, and following Labor's 2001 electoral defeat he was made Shadow Treasurer. In July 2003 McMullan was replaced as Shadow Treasurer by Mark Latham and relegated to the post of Shadow Minister for Finance, taking on additional responsibility for Reconciliation and Indigenous Affairs. When Latham became Leader he gave the job of Shadow Treasurer to his predecessor Simon Crean, despite having promised the job to McMullan. McMullan then became Shadow Minister for Finance and Shadow Minister for Small Business.