Accepting the presidential nomination at the Democratic National Convention, Mr Obama gave a more down-to-earth follow-up to his 2008 "hope and change" message. Weighed down by wars, high unemployment and political gridlock, he had a tone that was more subdued, less exuberant.
Mr Obama told Americans they face starkly different paths in choosing between him and Mr Romney in the November 6 election, saying his way may be hard but will bring economic renewal.
"America, I never said this journey would be easy, and I won't promise that now," he said. "Yes, our path is harder, but it leads to a better place. Yes, our road is longer, but we travel it together."
Locked in the political fight of his life with two months to go until the election, Mr Obama faces a challenge to recapture the magic of his historic campaign of four years ago and generate enthusiasm among voters who are weary of economic hardship.
The convention was Mr Obama's best chance to appeal to the nation until the presidential debates start in October.
Mr Romney professed himself not interested in watching the speech and his campaign dismissed the address as making the case for more of the same policies that have not worked for the past four years.
Mr Romney's campaign manager Matt Rhoades said: "Americans will hold President Obama accountable for his record – they know they're not better off and it's time to change direction."
Media reaction to the speech was not as glowing as it was for an address to the convention by former President Bill Clinton on Wednesday.
Mr Obama took a shot at Republican vice-presidential nominee Paul Ryan's plan to overhaul the Medicare health insurance plan by giving pensioners a limited amount of money through vouchers.
Leading up to Mr Obama's address, convention speakers played up his record, from ordering the mission that led to the killing of Osama bin Laden to lifting restrictions that barred gays from serving openly in the military.
"Ask Osama bin Laden if he's better off now than he was four years ago," Senator John Kerry said, feeding off Republican arguments that Americans are not better off under Mr Obama's leadership.
Mr Obama dismissed Mr Romney and Mr Ryan as "new to foreign policy", criticised a comment Mr Romney made that Russia is America's biggest geopolitical foe, and mocked Mr Romney for criticising London's handling of the Olympic Games.