The Democrat narrowly won his race in 2006, edging out incumbent Sen. George Allen.
"... after much thought and consideration I have decided to return to the private sector, where I have spent most of my professional life, and will not seek re-election in 2012," Webb said in a statement. "Notwithstanding this decision, I have every intention of remaining involved in the issues that affect the well-being and the future of our country."
U.S. Senator Patty Murray, chairman of the Democratic Senatorial Campaign Committee, said Webb "has been a strong senator and a true advocate for Virginia."
Murray added that Democrats "will field a strong candidate." But who will that candidate be?
There are rumors of a possible run by former governor Tim Kaine, who currently heads up the Democratic National Committee.
Former Gov. Tim Kaine, now DNC chairman (yes, he presided over those bad years), only ruled out a bid when failure to do so would have fired up speculation about Webb. A November 2010 poll had Kaine slightly outperforming Webb in a race against George Allen; Kaine, unlike Webb, will not have to worry about money. And any Democrat in the New South next year will have a second surge of African-American Obama voters boosting his chances.
So else will be in the race? Allen has already announced he's running for his old seat. But he's not the only one. Tea Party activist Jamie Radtke has also entered the race, and Bob Marshall, a leading conservative in the Virginia legislature, is considering a run, NBC Washington's P.J. Orvetti wrote last month.
But Allen’s biggest threat may come from Prince William Board of County Supervisors Chairman Corey Stewart, a likely candidate who would have the advantage of both conservative credentials and northern Virginia ties, Orvetti wrote.
Allen issued the following statement on Webb's decision not to run again:
“I respect Senator Webb’s service to our country and the very personal decision that he and his family have made. I did not enter into this race to run against any one person, but to fight for the families of Virginia to improve their opportunities in life. My campaign will continue to focus on achievable reforms that will help reinvigorate our economy, end reckless, runaway spending, and unleash our plentiful energy resources."
Meanwhile, Gov. Bob McDonnell released his own statement after Webb's decision was announced:
“Senator Jim Webb has spent his life serving our Commonwealth and our country. As a young Marine he bravely served on the front lines in Vietnam. Later he served his nation in the Reagan Administration, including a stint as Secretary of the Navy. Most recently his public service has come in the field of politics, representing the people of Virginia as a United States Senator. He cares deeply about this nation, and our future. I applauded his leadership in passing the Post-9/11 GI Bill expanding education benefits to veterans. I greatly appreciated his partnership and leadership in addressing the proposed closing of Joint Forces Command. Jim Webb puts his country first, and I thank him for the public service he has long provided, while looking forward to the continuation of that service, albeit in a different capacity, in the years ahead. I wish him, his family and his staff the very best."