A vigorous abortion opponent, the Kansas senator pledged to make "issues of life," fiscal restraint and tax reform key components of his effort to woo supporters.
"I have decided, after much prayerful consideration, to consider a bid for the Republican nomination for the presidency," Brownback said in a statement. "There is a real need in our country to rebuild the family and renew our culture and there is a need for genuine conservatism and real compassion in the national discussion."
Brownback said he has formed a presidential exploratory committee, which will allow him to travel the country and raise money while gauging support for the GOP nomination.
He also announced 20 members of his exploratory advisory committee, an eclectic mix ranging from anti-abortion activists to business executives, including: Domino's Pizza founder Tom Monaghan, former Major League Baseball commissioner Bowie Kuhn, and the Rev. Frank Pavone, head of the advocacy group Priests for Life.
Brownback has openly weighed a presidential bid for nearly two years, but has struggled to build a national profile despite more than a dozen trips to Iowa and other states with early nomination contests.
Still, he could influence members of the GOP's powerful conservative Christian wing skeptical of better-known, more moderate Republicans like Sen. John McCain of Arizona and former New York Mayor Rudy Giuliani, who also have established exploratory committees.
Nevertheless, Brownback's bid is considered a long shot in what is shaping up to be a nomination race led by better-known candidates.
The number of possible candidates with a claim to the GOP's social conservative wing has shrunk in recent weeks with the defeat of Sen. George Allen of Virginia in the midterm election and Senate Majority Leader Bill Frist's decision to forego a run for president.
Brownback said he plans to visit 10 states over the next month, starting in Cedar Rapids, Iowa, on Tuesday.
Brownback's chief of staff, Rob Wasinger, will take over the exploratory committee and the senator will begin building his organization and staff immediately, spokesman Brian Hart said. Plans call for Brownback to open his main offices in the Kansas City, Kan., area.
Despite his strong appeal among Protestant evangelicals and his Methodist roots, Brownback converted to Roman Catholicism in 2002 with the support of Sen. Rick Santorum, R-Pa., another prominent social conservative. He says his faith guides his opposition to abortion, gay marriage and embryonic stem cell research.
Brownback's faith also leads him to tackle social injustice around the world. He's spearheaded legislation to fight genocide in Sudan, cut down human slave trafficking and prison recidivism. Last week, he took an AIDS test with a potential White House rival on the Democratic side — Sen. Barack Obama of Illinois — to encourage others to be tested.
Brownback grew up on a farm near tiny Parker, Kan., where his parents still live. After receiving his law degree from the University of Kansas in 1982, he practiced law in Manhattan, Kan., and served as state agriculture secretary.
He was elected to the U.S. House in 1994 with the wave of Republicans who took control of both the House and Senate for the first time in 40 years. Two years later, he won a special election to succeed Bob Dole in the Senate after Dole left the seat to run for president.
Brownback, who promised to serve no more than two terms, has said he will not seek re-election in 2010.
Apart from McCain and Giuliani, other potential GOP contenders for the White House include Sen. Chuck Hagel of Nebraska, Gov. George Pataki of New York, Gov. Mitt Romney of Massachusetts, Gov. Mike Huckabee of Arkansas, Rep. Duncan Hunter of California and former Wisconsin Gov. Tommy Thompson.