The CBRE associate director will move in January following an internal restructure but will continue to be involved with a variety of North West projects.
The 13 regional offices, along with the South East business space division, have been re-branded as a national team.
Purdon will continue to specialise in the development sector, with a particular focus on land agency, mixed use, student residential and joint ventures and funding.
He said: "After 12-and-a-half years working in the North West, I feel that the time is right to broaden my horizons into new markets.
"The biggest challenge faced by both our public and private sector clients is how to finance development projects, given the restrictions in bank lending and the relative weakness of the occupier market.
"I believe that by relocating to London and expanding my contact base in the capital, I will be able to assist CBRE's clients to deliver against their objectives more successfully.
"I have thoroughly enjoyed my time in Manchester and look forward to broadening my experience and bringing a new dimension to my advice in the future."
John Ogden, managing director of CBRE North West, said: "Andrew has been a great addition to our development service and is well respected for his clear and commercially focused advice.
"He will continue to work with the Manchester team on specific projects and I look forward to seeing him further his career in the South East."