Wood joins from Passion, the agency he co-founded last year with Philip Slade and Kevin Doherty.
In his new role, Wood will lead the agency's planning department and work on the HSBC and Shell accounts. He replaces Dan Thwaites, who left earlier this month to go to Hicklin Slade & Partners.
During his career, Wood has worked at MRM Partners, where he led the Microsoft account and at Publicis, where he divided his time between London and Publicis Hal Riney in the US. During his 18 months at the network, he helped conceive the strategy for HP's "hype" campaign. Wood started his own agency in 2005, which has since merged with Pulse.
Jonathan Harman, the chief executive of RMG, said: "Magnus has robust relationship marketing skills, coupled with genuine brand understanding and the ability to find insights that drive response."
Wood added: "Planners should combine a curiosity about the world with an understanding of the relationship people have with brands and media, all combined with a passion for creativity. It is my intention to build such a team so that we have a greater impact on clients' business."