Paul Ryan, 42, said Republican presidential candidate Romney would "not duck the tough issues" if he won the White House, the Associated Press reported.
"After four years of getting the runaround, America needs a turnaround, and the man for the job is Gov. Mitt Romney," the Wisconsin lawmaker said in a speech, the full version of which was published by the Washington Post.
According to NBC, Ryan introduced himself to voters as the product of small-town, middle-class America and described Romney, the former Massachusetts governor, as a man whose "whole life has prepared him for this moment — to meet serious challenges in a serious way, without excuses and idle words."
The man who, according to NBC, has won plaudits from fellow Republicans for his understanding of the complexities of the US budget, added:
"Before the math and the momentum overwhelm us all, we are going to solve this nation’s economic problems... I’m going to level with you: We don’t have that much time. But if we are serious, and smart, and we lead, we can do this."
Ryan, chairman of the House Budget Committee, has devised a plan to curb long-term deficits with cuts in spending on everything from farm programs to education, and from remaking Medicare and Medicaid.
To often raucous applause, he also criticized Obama's economic policies, as well as his health-care reform initiative.
In comments that The New York Times interpreted as an attempt by Ryan to turn his relative youth to his Romney's advantage, Ryan said:
"College graduates should not have to live out their 20s in their childhood bedrooms, staring up at fading Obama posters and wondering when they can move out and get going with life. Everyone who feels stuck in the Obama economy is right to focus on the here and now. And I hope you understand this too. If you're feeling left out or passed by: You have not failed, your leaders have failed you."
Ryan went even further in attempts to appeal to the younger voters who flocked to Obama in 2008, the AP wrote, saying:
"I said, I hope it’s not a deal-breaker Mitt, but my playlist starts with AC/DC, and ends with Zeppelin."
Ryan's speech came after several notable members of the GOP, including Arizona Sen. John McCain and former Secretary of State Condoleezza Rice, took to the stage in Tampa Bay.
Presidents George W. Bush and George H.W. Bush also pledged their support, appearing in a video taped for the convention, NBC reported.
Romney delivers his acceptance speech Thursday night, the convention finale.