Weld's endorsement comes a day after former Bush Press Secretary Scott McClellan and the former Governor of Minnesota Arne Carlson, also a Republican, announced their support - separately - of Obama's candidacy.
"We need a president who will lead based on our common values and Sen. Obama demonstrates an ability to unite and inspire. Throughout this campaign I've watched his steady leadership through trying times and I'm confident he is the best candidate to move our country forward," he said.
As for McClellan, his preference for Obama was made public through a clip CNN distributed promoting a new TV program the network will debut tomorrow.
Appearing on "D.L. Hughley Breaks the News," McClellan said his vote is all about "change."
"From the very beginning I have said I am going to support the candidate that has the best chance for changing the way Washington works and getting things done and I will be voting for Barack Obama," he said to cheers and applause.
McClellan's decision isn't much of a surprise. His book "What Happened: Inside the Bush White House and Washington's Culture of Deception" showed McClellan's distaste with the partisan ways of Washington, DC -- not to mention W.
Not quick to embrace
McClellan's endorsement has received mixed emotions around the blogosphere.