New York Mayor Michael Bloomberg has left the Republican Party and changed his political status to unaffiliated.
The move has fuelled speculation that he may run as an independent candidate for the US presidency in 2008, although he insists he does not plan to stand.
Mr Bloomberg said a non-partisan approach had "worked wonders in New York". He is barred from seeking a third term as NY mayor in 2009.
A long-term Democrat, he switched parties when he ran for mayor in 2001.
Mr Bloomberg said on Tuesday: "Although my plans for the future haven't changed, I believe this brings my affiliation into alignment with how I have led and will continue to lead our city."
In recent speeches Mr Bloomberg has criticised partisan politics in the US, declaring it has paralysed decision making and jeopardised America's future.
The 65-year-old billionaire has enough money to finance a bid for the White House.
He is the founder of the media and financial data empire Bloomberg LP.
But analysts say that if he does run as an independent, he has little chance of success.
No independent has been voted into the White House in modern history.