"It has been one of the highest honors and privileges of my life to have served the people of Illinois in the United States Senate," he said in a statement released by his campaign Thursday.

"It is these Illinois families and their stories that will stay with me as I leave the United States Senate and begin the hard task of fulfilling the simple hopes and common dreams of all Americans as our nation's next president," Obama added.

Obama's Senate office will close sometime within the next two months.

His Senate staff will spend that time coordinating with his replacement, advising constituents with open requests, and archiving documents for Obama's presidential library.

Several Illinois Democrats, including Republican Jesse Jackson Jr. and Iraq war veteran Tammy Duckworth, a former congressional candidate who now serves in governor Rod Blagojevich's administration, have been mentioned as possible Senate replacements for Obama.

Blagojevich, who will appoint Obama's successor, announced last week that he was assembling a panel to vet likely candidates.

Obama was elected US Senate in 2004 and his replacement would be up for re-election in 2010.