Sen. Joseph Lieberman will announce on Wednesday that he will not run for re-election in 2012, NBC News reported on Tuesday.

Aides told NBC News that Lieberman made the decision around Thanksgiving but decided not to announce immediately due to the busy Senate schedule in December and his work leading the repeal of "Don't Ask, Don't Tell" also factored into his choice to keep this decision on "close hold."

Lieberman is holding a news conference about his plans in Stamford at 12:30 p.m.

An e-mail from one of Lieberman's press office staff members provided details of the planned event and aides told NBC News, "After many thoughtful conversations with family and friends over the last several months, Senator Lieberman made a decision about his future over the holidays, which he plans to announce on Wednesday."

He is expected to quote Eccliastes when he speaks today: "To every thing there is a season, and a time to every purpose under the heaven."

Aides acknowledge that a run for a fifth term representing Connecticut in the current political environment would have been difficult, that he recognized this would be a tough fight but strongly believes he could have won.

Lieberman has never shied away from a tough fight, but after 24 years in the Senate and 40 years in public life, aides said the senator believes it is time for a change.

Aides told the network that the senator has begun calling his friends, advisors and leadership to tell them about his plan not to seek re-election.

Lieberman, a long-time Democrat, was elected as an Independent in 2006 after losing the Democratic primary to Ned Lamont.

Since then, he has often sided with Republicans in the Senate, and there has been a lot of talk about whether Lieberman's next run would be as an Independent, Democrat or as a Republican.

In December, Lieberman told Andrea Mitchell, of NBC, that he still had some decisions to make.

"I've got a couple of decisions to make, and they're important ones to me and my family. The first one is, do I want to run again? I really love being a Senator. I feel good about what I've done, but every time you come to it, I think you've got to decide if you really want to do it for six more years," he said.

She also asked him about which party he'd run with.

"If I run again, it's more likely that I'll run as an Independent. But we'll see. We've got a lot of talking and thinking to do over the break with family and friends, and I hope to announce sometime early next year," he said.

A Lieberman aide told NBC that Lieberman does not know what his next chapter will include, but he plans to work the next two years "across party lines" and "put principle before partisanship."

Former Secretary of the State Susan Bysiewicz said on Tuesday she will seek the Democratic nomination for U.S. Senate in 2012.