Born in Champaign, Illinois, he graduated from Cornell University, London School of Economics, and Georgetown University Law Center. He practiced law throughout the 1980s and 1990s. He joined the United States Navy Reserve in 1989 and was recalled to active duty for the 1999 NATO bombing of Yugoslavia. He participated in Operation Northern Watch in Iraq the following year. He remains a member of the Navy Reserve, now holding the rank of Commander.
Kirk was elected to the House in 2000. During his fifth term in November 2010 he won a special election to finish the final months of former Senator Barack Obama's term and he began a six-year Senate term beginning in 2011.