Allen joins Lowe Worldwide as its vice-chairman in July and will work with Steve Gatfield, Lowe's worldwide chief executive, and Tony Wright, its worldwide chairman.
The appointment is a bid to boost Lowe's global presence. Gatfield said his responsibilities would include global marketing and business development and helping to reformulate Lowe's approach to the global market. He also described Allen's track record as "outstanding".
Before joining McCann, Allen was the chief growth officer for Interpublic and, before that, the executive vice-president and director of corporate development at McCann Group Worldwide. He is credited with being instrumental in global business wins including MasterCard and Siemens.
He was seconded to Lowe in 2004 to work on the winning pitch for Nokia.
Allen will be based at Lowe Worldwide's London office.
Allen said: "Lowe is well placed for future growth and I am thrilled to be working there once again."
Over the past year, Lowe Worldwide has halved in size and suffered management upheaval, including the departure of the Lowe London chairman, Paul Weinberger, and the agency's chief executive, Garry Lace.
Gatfield admitted: "We could do a lot better because we have a lot of talent and could organise that to greater effect."