No clear Democratic front-runners have emerged for Rockefeller's seat, but the announcement was made earlier enough for the party to find a candidate.
Though Obama is deeply unpopular here, that may not harm Democrats who attempt to succeed Rockefeller. Last fall, Obama lost every single West Virginia county in the general election, but voters still elected Democratic Gov. Earl Ray Tomblin and U.S. Sen. Joe Manchin. They also re-elected longtime Rep. Nick Rahall, D-W.Va., from the southern coalfields.
Democrats outnumber Republicans among registered voters 640,000 to 358,000, according to the Secretary of State's Office. But more than 222,000 people registered with no party affiliation.
Rockefeller, who was hailed for his role in shaping the Children's Health Insurance Program, later took heat from constituents for supporting the Affordable Care Act, Obama's overhaul of the nation's health care system.
He was a top backer of a so-called "public option" allowing the government to sell health insurance in competition with private industry, and pushed the Senate Finance Committee to a showdown vote on such a measure in 2009 — only to see it fail when fellow Democrats opposed it.
As his measure died, Rockefeller called the health insurance industry "rapacious."
"I'm proud of that work," he told The Associated Press in an interview ahead of his formal announcement. People may not like the idea of health care reform now, he said, but "the more it comes into effect, the more they will understand that it's good."
Rockefeller chairs the Senate Committee on Commerce, Science, and Transportation, and previously served at the helms of Intelligence and Veterans' Affairs. In that capacity, he helped persuade the Veterans Affairs Department to revisit disability claims arising from what has become known as "Gulf War Illness."
The great-grandson of famed industrialist John D. Rockefeller first arrived in West Virginia as a volunteer with the VISTA national service program in 1964. Within two years, he had won election to the Legislature, and then as secretary of state in 1968.
After a failed run for governor in 1972 and four years as president of West Virginia Wesleyan College, Rockefeller won his first term as governor. Toward the end of his second term, he narrowly captured the U.S. Senate seat of a retiring Jennings Randolph in 1984.
Rockefeller won by comfortable margins in each of his five terms in the Senate.
"Jay has built an impressive legacy, one that can be found in the children who have better schools, the miners who have safer working conditions, the seniors who have retired with greater dignity, and the new industries that he helped bring to West Virginia," Obama said in a statement.
Rockefeller hails from a family of achievers: In addition to the successes of his oil billionaire great-grandfather, the senator's father, John D. Rockefeller III, was a well-known philanthropist, while his uncle David Rockefeller ran Chase Manhattan Bank.
"There is no Rockefeller left, after Jay, in politics," said Fraser Seitel, a spokesman for David Rockefeller.
Smith contributed from Morgantown. Associated Press writers Lawrence Messina in Charleston, and Donna Cassata in Washington also contributed to this report.