Velluet, former EH assistant regional director (central and west London) and regional architect, will act as a consultant across architecture, conservation and planning.
Velluet has recently chaired both the steering and client groups overseeing the Westminster World Heritage Site management plan. He has also played a pivotal role in phase one of the Trafalgar Square project - part of the World Squares For All initiative.
A regular contributor to the architectural press, Velluet is a well-known speaker on building and area-based conservation. He also contributes to the debate on enhanced access to historic sites.
His expertise in conservation, development and planning proposals is regularly sought by property owners, developers and local planning authorities.
A spokesman for HOK said: 'Paul brings his exemplary expertise and skill to HOK's award-winning conservation team and will ensure projects of historical and architectural significance continue to be a fundamental part of our work for clients.'