Moving into a role as Romney's chief attack dog, Ryan declared Saturday that the nation under Obama's leadership is struggling through the "worst economic recovery in 70 years."
"No one disputes President Obama inherited a difficult situation," Ryan said, standing at Romney's side for the first time as the Republican presidential ticket on the USS Wisconsin, a retired battleship. "And, in his first two years, with his party in complete control of Washington, he passed nearly every item on his agenda. But that didn't make things better."
Romney selected the 42-year-old Ryan, a seven-term congressman, from a short list that included Ohio Sen. Rob Portman, former Minnesota Gov. Tim Pawlenty, Florida Sen. Marco Rubio and Virginia Gov. Bob McDonnell.
Ryan is the architect of a conservative and intensely controversial long-term budget plan to remake Medicare and cut trillions in federal spending.
His selection immediately thrusts those budget plans into the forefront of the presidential contest.
Obama campaign manager Jim Messina called Ryan is the "architect of the radical Republican House budget" proposal and said the plan "would end Medicare as we know it."
"We won't duck the tough issues," Ryan said. "We will lead."
The congressman blamed Obama for the nation's unemployment rate that has exceeded 8 percent for more than three years, the longest run since the Great Depression.
"Higher unemployment, declining incomes and crushing debt is a not a new normal. It is a result of misguided policies," Ryan said.
Romney initially made his announcement to supporters via a phone app. "Mitt's Choice for VP is Paul Ryan," it said and implored backers to spread the word.
One campaign official said Romney had settled on Ryan as his pick on Aug. 1, more than a week ago, and informed Beth Myers, the longtime aide who had shepherded the secretive process that led to the selection. The official spoke on condition of anonymity to provide details.
Ryan is chairman of the House Budget Committee, and primary author of conservative tax -and-spending blueprints that the tea party-infused Republican majority approved over Democratic opposition in 2011 and again in 2012.
It envisions transforming Medicare into a program in which future seniors would receive government checks that they could use to purchase health insurance. Under the current program, the government directly pays doctors, hospitals and other health care providers.
Ryan and other supporters say the change is needed to prevent the program from financial calamity. Critics argue it would impose ever-increasing costs on seniors.
Other elements of the budget plan would cut projected spending for Medicaid, which provides health care for the poor, as well as food stamps, student loans and other social programs that Obama and Democrats have pledged to defend.
Ryan's budget plan died in the Democrat-controlled Senate.
"Our rights come from nature and from God, not government," Ryan said. "That's who we are. We promise equal opportunity, not equal outcomes."