"The state has consistently spent more money each year than it receives in revenue. That obviously cannot continue. To stop the bleeding, before it's too late we must impose fiscal discipline, and make tough decisions," said Ryan.
Ryan's announcement comes seven years after leaving politics following a loss to Rod Blagojevich.
The 63-year-old has promised not to raise income or sales taxes if elected governor, despite budget problems so severe that next year's budget deficit could reach $12 billion.Six other republicans are running for governor: businessman Adam Andrzejewski; state senators Bill Brady and Kirk Dillard; former state GOP chairman Andy McKenna; consultant Dan Proft; and DuPage County board chairman Bob Schillerstrom.
The Associated Press contributed to this report.