The state treasurer, a Democrat, wants Pres. Barack Obama's former Senate seat, which is currently occupied by Roland Burris. Burris is not running for election.
Giannoulias says he would work for reform in Washington, if elected. In fact, the theme of his campaign is one of reform and promise, a promise to fight for the rights of everyday people and to revive the economy and to restore opportunity.
It appears Giannoulias intends to try to capitalize on his association with President Obama, while attempting to link Republicans to the country's economic problems.
Some say the Chicago announcement makes Giannoulias the leading contender in February's Democratic primary.
"Alexi Giannoulias said several months ago that he was looking at running for the U.S. Senate, and that's the kind of commitment we need from someone filling this all-important seat," said Democratic State Sen. Kwame Raoul, who represents the 13th District.
Other Democrats eyeing a potential Senate run include former spokesperson for ousted Gov. Rod Blagojevich and Chicago Urban League head Cheryle Jackson and Chicago businessman and son of the late Sen. Robert Kennedy, Chris Kennedy.
Giannoulias, a wealthy banking heir, says he will refuse contributions from corporate pacs and federal lobbyists. He also took North Shore Republican Mark Kirk to task. Kirk declared his GOP candidacy last week.
"Just this week, we heard a Republican candidate for this very office pledge reform with one hand, while the other hand takes millions from corporate special interests," the state treasurer said.
During his speech, Giannoulias made several references to President Obama, whom Giannoulias called a friend and a mentor. The two remained basketball buddies after Giannoulias' family's Broadway Bank helped raise seed money for Obama's winning 2004 Senate bid.
And although critics give Giannoulias credit for modernizing the state treasurer's office and helping ousted Hartmarx workers, questions may resurface about losses suffered by a college savings plan overseen by his office and questionable loans made by his family's bank.
"He's already proven that when it comes down to dealing with those financial issues, he is more than capable to get it done," said Democratic State Rep. Susana Mendoza of the 1st District.
Giannoulias' decision to run comes after Illinois Attorney General Lisa Madigan opted for re-election rather than seek a Senate bid, something the White House supported, supposedly.
Sen. Roland Burris, who was appointed to the position by Blagojevich, has decided not to seek a full term but gives no endorsement to anyone, at least not yet.
"I have 18 more months to serve in the U.S. Senate, and I will be working as a United States senator as long as the taxpayers are paying my salary," Burris said.
Republicans view the Illinois senate Seat as up for grabs and as a chance for them to stage a comeback.
After announcing his candidacy, Democrat Giannoulias was set to begin a three-day tour of the state. Campaign insiders say he has already raised more than $2 million for the election effort.