Croot (pictured) has 25 years of experience in media and comms, with previous roles including group head of media relations at Barclays.
He spent 10 years as a director at Brunswick and before that was news editor at ITN.
News of Croot's appointment follows the merger earlier this month of Newgate owner Porta and Italy-headquartered SEC to form SEC Newgate.
Newgate CEO Emma Kane said: "Giles has incredible experience, both as an advisor and leading in-house teams. I’m delighted he’s chosen to join the team at Newgate at a very exciting time for the evolution of our business."
Croot said: "The media, social and political environment is changing rapidly – businesses and their leaders are no longer judged primarily by the profit they deliver. With investors, employees and customers all expecting higher standards from the businesses they support, business leaders must deliver high-quality, integrated communication. The team at Newgate is expert at doing this, which is why I’m so looking forward to working with them and helping our clients to succeed."