Porter joined the newspaper as political editor in 2007, having previously worked as the deputy political editor at The Sun and The Sunday Times. He was made public policy editor at the Telegraph last month, while Robert Winnett became political editor.
Porter joins Brunswick as a director and is expected to start in his new role in the New Year.
He told PRWeek: ‘Having been a political and business journalist for 15 years, I am keen to move on to the next stage of my career. Working for The Daily Telegraph has been a privilege and I have crammed an awful lot into four years as political editor. Now I want to use the experience I have gained in the private sector.
‘The opportunity presented by Brunswick is incredibly exciting and I am looking forward to starting.’
It is thought that he will draw on his experience as a business journalist, including a stint on Sunday Business, to work across a range of Brunswick’s clients, rather than in a specialist public affairs role.
Porter joins a number of former political editors that have moved to the agency world, including Portland’s George Pasco-Watson, formerly of The Sun and TLG director and former Sunday Times political editor Jonathan Oliver.