He declared that "with able leadership, America's best days are still ahead," vigorously asserting that President Barack Obama had failed to provide it.
The Republican, who has been plotting a comeback since losing the GOP presidential nomination to John McCain three years ago, offered himself as the person best able to lead a country struggling to recover from economic crisis.
"It is time that we put America back on a course of greatness with a growing economy, good jobs and fiscal discipline in Washington," Romney, a former venture capitalist with a record of turning around failing companies, said in a video posted on his website and on Facebook. He also announced the formation of the committee, which will allow him to raise money, in a Twitter message.
Romney's move had been expected and a full-fledged campaign is a near certainty. He has traveled across the country to meet in private with donors and sound out their support. His political committee's headquarters near Boston has been bulking up. And in his few public appearances, he has honed his criticism of Obama.
Romney's strengths are substantial: He's well known and he's an experienced campaigner. He has a personal fortune and an existing network of donors. He has a successful businessman's record.
But his challenges are big, too. They include a record of changing positions on social issues including abortion and gay rights, shifts that have left conservatives questioning his sincerity. He also has struggled to allay some skeptics of his Mormon faith.
Romney oversaw a health care law that was enacted in Massachusetts on his watch that's similar to Obama's national health overhaul, which conservatives despise. His announcement video didn't mention either law.
He invested more than $40 million of his own money in the 2008 race and counted on early wins in Iowa and New Hampshire that never materialized. He tried to run to the right of the pack but couldn't persuade enough GOP primary voters.
Yet Romney is the closest the Republicans have to a front-runner. Former Minnesota Gov. Tim Pawlenty has also taken the initial steps toward a White House run, setting up an exploratory committee. Former House Speaker Newt Gingrich is laying the groundwork for an early-May announcement.
Mississippi Gov. Haley Barbour, former Sen. Rick Santorum of Pennsylvania and Minnesota Rep. Michele Bachmann are also putting together political machines for potential presidential runs.
All are auditioning for the chance to take on Obama, who is seeking a second term asking voters to let him finish the job he won in 2008. An ailing economy and an anxious electorate both dog the president, who won election on the promise of change but now has a record that defines him.
Romney hammered Obama's stewardship of the economy and offered a preview of his expected campaign theme: He is a proven business executive while Obama remains unqualified to repair a fractured economy.
"President Obama's policies have failed. He and virtually all the people around him have never worked in the real economy. They just don't know how jobs are created in the private sector."
Then Romney makes the case for himself.
"From my vantage point in business and in government, I have become convinced that America has been put on a dangerous course by Washington politicians, and it has become even worse during the last two years," he said. "But I am also convinced that with able leadership, America's best days are still ahead."
Romney, the son of a former governor of Michigan, met his future wife when he was 18 and she was 15, just before he departed for college and then more than two years of Mormon missionary work in France. The couple had five sons, while Mitt Romney went on to earn millions as a business consultant and venture capitalist.
While heading Bain Capital, he helped launch the Staples office supply chain, as well as buy Domino's Pizza.
His public career began in 1999, when he was recruited to take over the 2002 Winter Olympics after scandal and financial deficits threatened the Salt Lake City games.
In 2003, he took over as governor of Massachusetts after a campaign in which he cast himself as a moderate on abortion, gay rights and stem cell research. He had sounded many of the same themes during an unsuccessful 1994 U.S. Senate race against Democrat Edward M. Kennedy.
He chose not to seek a second term and instead turned his sights to the White House.
Romney invested more than $40 million of his own money in the 2008 race and counted on early wins in Iowa and New Hampshire that never materialized. He tried to run to the right of the pack but couldn't persuade GOP primary voters to overlook his reversals on social issues including abortion and gay rights. He also struggled to allay skeptics of his Mormon faith.