The new firm, which is yet to be named, will be based in London. He will continue to work as an adviser to Maitland for his client, hedge fund Marshall Wace, in the short term.
Trefgarne had been a partner at Maitland for the past six years. He was previously director of media at oil giant BP – and turned down the opportunity to return to BP in a global role in 2012 – and before this spent 11 years at The Telegraph as an economics and political commentator.
Trefgarne said: "I am leaving Maitland after six happy years because I think the financial PR market is changing. There are a handful of top-tier firms, but increasingly we are seeing the emergence of independent and specialist boutique businesses alongside them. I see this as an opportunity."