As revealed on prweek.com/uk, Ed Williams will leave the BBC in early October to join Edelman as UK CEO.
A former director at City agency Brunswick, he makes the move after three years heading up comms at the BBC, where he is said to be a key lieutenant of director general Mark Thompson.
The news comes as BBC Trust chairman Lord Patten launches plans to cut the pay of senior BBC executives.
Last September, Williams featured in a list of public sector employees earning more than £100,000 a year, produced for the BBC's Panorama programme.
The comms chief was among the highest earners, with a salary of £225,940.
One BBC insider said that Williams' exit would be a blow to the corporation: 'He's just about the best connected man, and he's also extremely ambitious.
'His loss will be felt by Mark Thompson, who has got a huge amount of respect for Ed's professional ability. His going does leave a significant gap.'
Williams recently returned from two months studying advanced management at Harvard Business School in Boston, paid for by the BBC.
BBC sources indicated that the corporation will seek a replacement for Williams from within.
In the new role, Williams will report to EMEA CEO Robert Phillips, who held the UK CEO post until being promoted to his current role in January.
About Ed Williams
Williams started his career in journalism, spending four years as news editor of GMTV
He joined the BBC as director of comms in 2008, having been director of comms at Reuters and a director at Brunswick for five years
Aided by recently-departed chief spokesman Donald Steel, Williams has steered the BBC through issues such as the licence fee settlement and Sachsgate.