Perry ran unsuccessfully for president against Romney but has since endorsed the ex-Massachusetts governor.
He said in a statement Saturday that Ryan underscores Romney's "commitment to downsizing Washington, fixing our economy and restoring American job creation."
Perry said previously he wasn't interested in being a GOP vice presidential candidate. But he also was never considered a serious contender for Romney's choice.
The governor was at the Iowa State Fair on Saturday on Romeny's behalf.
His statement called Ryan an exciting choice who will "energize economic voters, young voters and blue collar voters" while solidifying the Republican Party's commitment to fiscal responsibility.