Perkins has held senior comms roles for the royal household for the past seven years. He was appointed comms secretary to William, Kate and Prince Harry two years ago.
He led comms on the birth of Prince George, on the Cambridges' tour of Australia and New Zealand this year, and most recently Prince Harry’s Invictus Games in London.
Perkins will take up his new role at Portland in October as a senior adviser and will work across the company’s UK and international clients.
Perkins said: "I am absolutely delighted to be joining Portland at a particularly exciting time for the firm, especially in the international arena. It has been an extraordinary privilege and great pleasure to work for the royal family over the past seven years and I look forward to applying some of that knowledge and experience in my new role."
Perkins became assistant press secretary to the Queen in 2007, and served as press secretary to the Duke of York. He went on to become deputy press secretary to the Queen and head of news at Buckingham Palace for the Queen's Diamond Jubilee year.
During his time with the royal household, he has co-ordinated media on royal engagements in 25 countries across Europe, North America, Africa, Australasia, the Middle and Far East.
Perkins began his career as a journalist, spending eight years in television news at the BBC Six O'Clock News, and the ITV Evening News.
Portland managing director Tim Allan added: "Very few people have managed communications for such truly global figures as the royal family, let alone combined this with a career as a senior broadcast journalist. Ed will bring a huge wealth of experience to Portland’s clients, whether they are high profile individuals, companies or international bodies. We are delighted to have him on board."