"Here is our pledge: We will not duck the tough issues, we will lead," the Wisconsin representative said in his acceptance speech Wednesday at the Republican National Convention in Tampa, Fla.
Shouting over the crowd's applause and cheers, Ryan said: "All of us can do this. Together we can do this. We can get this country working again."
He referred to his wife, children, parents and grandparents in his speech, quoting his father as telling him "You have a choice: You can be part of the problem, or you can be part of the solution."
The Obama administration has made its choice, he said, "and Mitt Romney and I have made ours: Before the math and the momentum overwhelm us all, we are going to solve this nation's economic problems."
"And 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," the House Budget Committee chairman said.
Ryan, 42, laced his remarks with withering comments about President Obama's policies and campaigning.
"I have never seen our opponents so silent about their record and so desperate to keep their power," Ryan said. "They've run out of ideas. Their moment came and went. Fear and division are all they got left."
The congressman said Obama's administration began with stirring speeches and optimism.
"Now, all that's left is a presidency adrift ... like a ship trying to sail on yesterday's wind," he said.
Ryan said he and Romney welcome a debate on the Affordable Care Act, which Republicans have been calling "Obamacare," and the threat the GOP says it poses to the future of Medicare.
"The greatest threat to Medicare is Obamacare and we're going to stop it," Ryan said. "Medicare is a promise and we will honor it. A Romney-Ryan administration will strengthen Medicare."
As the country pushes toward $16 trillion in debt, Obama has done "nothing," Ryan charged.
"They have no answer to this simple reality: We need to stop spending money we don't have," he said.
The Romney-Ryan ticket has a plan to build a stronger middle class and a goal of generating 12 million jobs over the next four years.
"We also will keep federal spending at 20 percent of [gross domestic product] or less because that's enough," Ryan said.
"The choice is whether to put hard limits on economic growth or hard limits on government and we chose to limit government," he said.
A Romney-Ryan presidency "will speak with confident and clarity" on the global stage.
"[We] will act in the conviction that the United States is still the greatest force for liberty that this world has ever known," he said.
Concerning the state of the nation, Ryan said, "None of us have to settle for the best this administration offers -- a dull, adventureless journey from one entitlement to the next, a government-planned life, a country where everything is free but us."
"Listen to the way we're spoken to already," he said, "as if everyone is stuck in some class or station in life, victims of circumstances beyond our control, with government there to help us cope with our fate."
That message is the opposite of what he learned when growing up in Janesville, Wis., or going to college in Ohio and working odd jobs to earn money.
"I was on my own path, my own journey, an American journey where I could think for myself, decide for myself, define happiness for myself. That's what we do in this country. That's the American dream," Ryan said. "That's freedom, and I'll take it any day over the supervision and sanctimony of the central planners."
Ryan said he and Romney share the same moral creed.
"We believe that in every life there is goodness; for every person, there is hope. Each one of us was made for a reason, bearing the image and likeness of the lord of life," Ryan said. "We have responsibilities, one to another -- we do not each face the world alone. And the greatest of all responsibilities, is that of the strong to protect the weak."
Each belief is essential to a democratic government, Ryan said. They are unchanging and "sometimes, even presidents need reminding, that our rights come from nature and God, not from government."
In closing, Ryan said: "Whatever your political party, let's come together for the sake of our country. Join Mitt Romney and me. ... Let's get this done."