Bloomberg, 76, has been a political independent since abandoning his Republican Party registration in 2007. He has said he is considering running for president as a Democrat -- making this one of his most overt moves to date toward a possible White House campaign.
“Today, I have re-registered as a Democrat -- I had been a member for most of my life -- because we need Democrats to provide the checks and balance our nation so badly needs,” Bloomberg said.
Bloomberg is the founder and majority owner of Bloomberg LP, the parent company of Bloomberg News.
Bloomberg was elected mayor of New York City as a Republican in 2001 and re-elected in 2005. He announced in 2007 he was changing his registration to be unaffiliated with a party and won a third four-year term as an independent in 2009.