Lieberman earned the scorn of the Democratic party years ago when he embraced Republican tenets. He was a speaker at the 2008 Republican National Convention and was considered a possible running mate for his friend, Sen. John McCain. He was Al Gore's vice presidential running mate on the Democratic ticket in 2000.
Lieberman, 70, ended his 24 years representing Connecticut quietly and reflectively, The Washington Post reported Thursday.
"I regret to say as I leave the Senate that the greatest obstacle that I see standing between us and the brighter American future we all want is right here in Washington," he told the near-empty chamber Wednesday. "It's the partisan polarization of our politics which prevents us from making the principled compromises on which progress in a democracy depends."
He tried to push back against the bitter partisanship that developed in the Senate, but at a high price. Lieberman was drummed out of his party -- he won as an independent in 2006 after losing the Democratic primary -- and chose to retire at the end of his term rather than face the prospect of losing. Despite falling from favor with Democrats, he still caucused with them, creating a rift between him and Republicans.
Lieberman appealed to his colleagues to "support, when necessary, the use of America's military power" and "have the patience and determination when the public grows weary to see our battles through until they are won," the Post said.
He also reminisced about his years in the Senate.
"When I started here in the Senate," he said, "a blackberry was a fruit and tweeting was something only birds did."