Bennett is set to take GA's top UK post in May when he will also join the agency's European management board.
The news comes just a week after GA announced former London CEO Mark Popiolek was stepping down from the role after a European reshuffle, that saw Frankfurt office CEO Michael Kruesmann become head of Europe (PRWeek, 1 March 2001).
On his decision to quit The Sunday Telegraph, Bennett said: 'I always wanted to run my own business.'
He added: 'This is a great time to move into financial PR because it looks like we are going to have a recovery soon. There's going to be a lot of new deals and clients reviewing PR and a lot of opportunities.'
Bennett said 'all major financial PR firms' had approached him in the past but he was attracted by the challenge at GA: 'It is arguably the biggest corporate and financial agency in the world, but not in the UK.'
Bennett has had a distinguished City career, working at The Times as deputy business editor prior to his appointment at The Sunday Telegraph.
GA London chairman and worldwide executive vice-chairman Howard Lee hinted at changes to come in the London office.
'Our parent firm Omicom is very supportive of developing our business and Neil's appointment is evidence of that,' he said.