Arc Seven Communications has been launched by Alistair Clay and already has a number of clients including the London Housing Foundation, development charity Plan International and disability charity Limbcare.
Before working at children's charity Plan UK, Clay spent five years as a news reporter on the Daily Mirror and worked as a features writer at Teletext.
He is joined by Gemma Keogh, who most recently worked at the Three Faiths Forum as project co-ordinator.
Clay said the agency would focus on 'holistic comms solutions', including media relations, digital and SEO.
He added: 'Charities often forget who their audience is. It's about challenging them to think from the point of view of the new supporter or new donor.'