Luke Bozier, a former senior Labour adviser and co-author of the Labour Business report, has defected to the Conservatives.
In a blog Bozier said the death of new Labour was "tragic" and that he believed the party was no longer electable.
"Ed proudly declared that New Labour is dead; how tragic. With it, the passion for reform that made our party electable has gone. So too has the pro-business, pragmatic approach to wealth and enterprise. Instead there is a vision and leadership vacuum. At a time when the nation needs strong political leadership, Labour offers nothing. Labour seems to have learned nothing from the days of Brown."
Bozier wrote that Labour's future looked "bleak" and said David Cameron's Conservatives had become "the party of the aspirational classes".
"Aspiration is what took me from a council estate in South Wales to start my own business and to political activism."
The 27-year-old former e-campaigns manager worked with Tony Blair in developing an online strategy and runs his own business.
His defection was greeted by Tory MP Louise Mensch, who tweeted "Hope other Blairites consider following him. Labour has changed."
It comes after a difficult start to the year for the Labour party. Over the weekend, they attempted to regain the political initiative with shadow chancellor Ed Balls accepting he could not pledge to reverse any of the coalition's cuts.