Simon will start in his new role in May, advising national and local governments, multinational corporates and international foundations.
He will be based in London where he will support Portland’s digital work with clients around the world, alongside Portland's teams in New York, Washington DC, Doha and Nairobi.
Simon has been working at Number 10 since March 2013. He is responsible for all digital comms and engagement for the Prime Minister, Deputy Prime Minister and Cabinet Office, including cross-government campaigns.
He currently leads a team of 15 campaigners, content editors, technical staff and film-makers. Simon is also deputy director of the Government Communication Service overseeing improving standards, capability and delivery of digital comms across all government departments.
Simon has previously worked at the Central Office of Information, and as a digital specialist and journalist at the BBC.
He said: "After four years working in the heart of Government at Number 10, I feel now is a good time to help Portland deliver the very best offering to its clients in a rapidly evolving digital and social media landscape."
Mark Flanagan, senior partner for content and digital strategy, added: "Anthony has been a driving force behind the UK Government’s use of digital in its communications and we are delighted that he has chosen to join Portland as we continue to grow. His skills and experience will massively benefit our clients as they adapt to the changing nature of communications."