Acevo has joined the majority of its members as a registered charity after 19 years operating as a company limited by guarantee.
Chief executive Stephen Bubb said the decision was a "point of principle" that he thought might surprise members. "The amusing thing about it is that most people think we already are a charity," said Bubb. "The main driver behind this is the fact that the majority of our members are registered charities and, as their professional body, it's an appropriate legal form for us to take."
He added that Acevo would now get rates relief, but the decision was not taken for financial reasons.
David Hunter, policy officer at Acevo, said the professional body, which has more than 2,000 members, should practise what it preached on this issue.
"If we're representing charities and espousing their causes, this gives us more credibility," he said.
Andrew Hind, chief executive of the Charity Commission, said: "Promoting the voluntary sector for the benefit of the public is a charitable purpose that is increasingly relevant to supporting today's community-based organisations.
"Acevo carries out valuable work in support of the third sector, and we welcome its transition into a registered charity."