Sen. Bill Frist won't make a bid for the White House in 2008, the Tennessee Republican announced Wednesday.

"In the Bible, God tells us for everything there is a season, and for me, for now, this season of being an elected official has come to a close. I do not intend to run for president in 2008," Frist said in a statement.

The heart and lung transplant surgeon who is retiring from the Senate after serving the last four years as Senate majority leader said he plans to resume regular medical missions around the world "to serve those in poverty, in famine and in civil war." He also plans to "be a strong voice to fix what is broken in our health care system and to address the issues of clean water and public health globally."

Frist is ending a 12-year run in the Senate, where he was influential in passage of the Patriot Act, Medicare prescription drug legislation, establishment of a $15 billion Global HIV-AIDS initiative and a clean water bill aimed at eradicating the leading killer of children worldwide.

In the Senate, Frist rose through the Republican ranks on conservative social principles. He helped get confirmed Supreme Court justices John Roberts and Samuel Alito.

In 2005, he was a key defender of Bob and Mary Schindler, the parents of brain-damaged woman Terri Schiavo, who was taken off a feeding tube at the request of her husband, Michael Schiavo, despite the Schindlers' objections. Frist sponsored legislation signed by President Bush to allow the case to be reviewed by federal courts. The courts ultimately rejected the parents' wishes. A majority of Americans opposed Republican interference in the case.

Frist pledged to his constituents leave the Senate after serving two terms, and said Wednesday he has never thought to deviate from that plan.

Frist had no experience in politics when he defeated Democratic Sen. Jim Sasser to win his Senate post. He said he and his wife, Karyn, are looking forward to returning to private life in Tennessee.

"Politics for us was never an end — it was a means — a means to serve our country and humanity, to improve lives. And for that opportunity I am truly grateful," Frist said.

Outgoing Republican National Committee Chairman Ken Mehlman said Frist is the "very definition of a public servant.

"Whether it’s saving lives through performing surgery in Africa or helping craft new laws to save Americans from terrorists, Bill Frist’s dedication, principles, creativity, and compassion have made America a more prosperous place and the world a more decent place,” Mehlman said in a written statement.

Though Frist had previously flirted with the idea of a presidential run, much of that plan appears to have been scuttled even before Republicans lost the Senate majority in the midterm. He has frequently polled below fellow Republican potential presidential contenders like Arizona Sen. John McCain and former New York City Mayor Rudy Giuliani.

Frist leaves behind him a long list of potential contenders considering a presidential campaign, and with his political action committee, VOLPAC, still has the ability to offer financial assistance to his preferred candidate.

Other frequently named potential Republican contenders in 2008 include Govs. Mitt Romney of Massachusetts, Mike Huckabee of Arkansas and George Pataki of New York, Sens. Sam Brownback of Kansas and Charles Hagel of Nebraska and Rep. Duncan Hunter of California.

FOX News' Trish Turner contributed to this report.