The PRCA found that 58 per cent of PROs surveyed thought the Games succeeded well beyond expectations.
The results come at the end of the Games, in which Great Britain came third in the medal table.
Fifty-eight per cent of senior in-house and agency figures polled also said they thought the Games had a 'very positive effect' on Britain's international reputation. None said it had either a negligible or negative effect.
PRCA CEO Francis Ingham said: 'These figures are astonishing in their uniformity. Not only were the Games a triumphant success, exceeding expectations, they have also delivered a significant boost to the UK's international reputation.'
Super Saturday, when British athletes including long-distance runner Mo Farah and heptathlete Jessica Ennis picked up gold, topped the list of PROs' favourite moments, with 37 per cent of the vote.