The support from Bush came the day after a key Tea Party group, FreedomWorks, said it was ending its opposition to Romney, considered a sign by some political observers that Republicans are starting to coalesce around the former Massachusetts governor, The Washington Times reported.
Bush said in a written statement that Romney was the kind of believer in "entrepreneurial capitalism" the nation needed to get the U.S. economy back on track, The Hill reported.
"We face huge challenges, and we need a leader who understands the economy, recognizes more government regulation is not the answer, believes in entrepreneurial capitalism and works to ensure that all Americans have the opportunity to succeed," Bush said.
Bush -- the brother of former U.S. President George W. Bush -- said Romney had proven his electability through the primary campaign and urged the GOP to rally behind him.
Romney had received the endorsement of Bush's father, former President George H.W. Bush, in December.
The Hill noted Jeb Bush had been considered a potential late entry into the race if the Republicans could not decide on a consensus nominee to challenge President Barack Obama before the GOP National Convention in August.
Romney, however, has been gaining momentum in the primaries. He won Jeb Bush's state of Florida and bagged the Illinois primary Tuesday.
FreedomWorks, an influential Tea Party group led by Dick Armey, a former U.S. House majority leader from Texas, made it known Tuesday it no longer opposes Romney, though it isn't endorsing him, the Times reported.
"It is a statistical fact that the numbers favor Mitt Romney," FreedomWorks Vice President Russ Walker told the Times. "We are dedicated to defeating Obama and electing a conservative Senate that will help Romney repeal Obamacare and address the nation's economic and spending challenges."
Romney has more than half the delegates he needs to capture the GOP nomination.
"We have members that supported all the candidates, including Mitt Romney," Walker said. "Each of the candidates has weaknesses and strengths."
The Tea Party, he said, is a "leaderless movement, so it will be up to individuals to decide when and where they put their support."