Bennett leaves after 18 months in the post, designed to champion the work of RDAs and to lobby Whitehall on their behalf.
He is to become a freelance consultant on regeneration, enterprise and economic development issues for the public and private sector. The former Luther Pendragon senior consultant was the first holder of the post, created to beef up comms when the RDA's funding formula changed to give regions more flexibility on budget allocation.
The National Secretariat gives advice to the UK's nine RDAs. Bennett said that while each has its own economic strategy and development targets, there were areas where shared best practice was advantageous.
Bennett's exit comes two months after the RDAs took on responsibility for governmental local advisory service Business Link. Showing how this service will develop will be one of the challenges facing Bennett's successor.
The post also demands strong regional and trade press relations.
RDAs agree economic growth targets with the Government and private sector partners. Last year, the East of England and East Midlands RDAs failed to meet their targets.