"I am taking this step because we have to repair the damage that's been done to our country over the last six years," said Richardson, a former congressman, U.N. ambassador and Energy Department secretary.
"Our reputation in the world is diminished, our economy has languished, and civility and common decency in government has perished," he said in a statement.
His entry would make the Democratic race the most diverse presidential contest in history. Beside Richardson's bid to be the first Hispanic chief executive, Sen. Barack Obama would be the first black president and likely candidate Sen. Hillary Rodham Clinton would be the first female president.
Richardson, 59, is a former congressman, U.N. ambassador and Energy Department secretary. He brings a wealth of experience in international affairs that has extended even into his governorship of a small but politically important swing state.
He has hosted talks on North Korea's nuclear program in New Mexico and most recently traveled to Sudan to meet with the country's president to press him for an end to the bloodshed in Darfur.
Despite having one of the most varied and impressive portfolios in politics, Richardson enters the race as an underdog. Polling in early voting states shows him ranking near the bottom in a very crowded Democratic field led by Clinton, Obama and 2004 vice presidential nominee John Edwards.
Richardson does not have the national fundraising network of some of his rivals in what is bound to be a very expensive race. And he'll have to spend the next two months concentrating on a legislative session in Santa Fe instead of campaigning.
But Richardson's decision to form an exploratory committee will allow him to begin raising money and putting together his campaign organization. A decision on whether to formally enter the race is expected in the spring.
William Blaine Richardson was born in Pasadena, Calif. His father was an international banker from Boston; his mother was Mexican. He spent his early childhood in Mexico City, where his father worked for Citibank. As a teenager, he attended a tony boarding school in Concord, Mass., where he was pitcher on the baseball team — a sport he follows closely to this day.
After graduating from Tufts University in 1971 with a master's degree in international affairs, Richardson worked first as a congressional aide and then for the State Department under Henry Kissinger. He was a staffer for the Senate Foreign Relations Committee when he decided to leave Washington in 1978 to launch a political career.
Richardson settled in New Mexico, partly because of the state's large Hispanic population. In 1980, after only two years in the state, he surprised political experts by coming within 1,000 votes of unseating veteran Republican Rep. Manuel Lujan, who would later serve as Interior Secretary. In 1982, Richardson was elected to the House from New Mexico's newly created 3rd Congressional District. He was re-elected seven times, becoming a member of the Democratic leadership.
Richardson was disappointed that President Clinton didn't select him for Secretary of State. However, Clinton did tap Richardson to be U.S. Ambassador to the United Nations in 1996, where he served until 1998, when he joined the Clinton cabinet as Secretary of Energy. He was criticized by Congress during his two years at the helm of the Energy Department for his handling of alleged breaches of nuclear secrets and the botched case against Los Alamos scientist Wen Ho Lee.
After leaving the federal government in 2001, Richardson worked briefly for Kissinger's consulting firm and served on the boards of several corporations while preparing another campaign for public office.
He was easily elected governor of New Mexico in 2002 and re-elected in November with 68 percent of the vote. While governor, Richardson has continued to keep a high profile nationally and served as chairman of the Democratic Governors Association as it expanded its ranks with wins across the country.