PR budgets received a minus 1.7 per cent reading in the survey, which measures the balance of companies revising spend upwards against those revising spend downwards in the July to September period.
Overall marketing budgets were revised upwards by a net 12.3 per cent of companies, which was the strongest rate in 13 years and the fourth consecutive quarter above zero.
The internet continued to enjoy the greatest boost of any marketing channel (up 11.7 per cent) but main media advertising staged a comeback with its strongest reading in three years (up 3.4 per cent).
IPA director-general Paul Bainsfair said the report provided "a welcome boost to our industry" while Chris Williamson, chief economist at Markit and the author of the report, said it added to the flow of upbeat data on the economy.
"Marketing spend looks set to rise sharply as companies boost their budgets to an extent not seen in the 13-year history of the survey," he added.
Other sectors joining PR in the doldrums in Bellwether Q3 include direct marketing (down 3.4 per cent), market research (down 3 per cent) and events (down 1.1 per cent).
PR had put in a stronger performance in Bellwether reports in the first half of the year. In the second quarter it had a positive reading of 3.4 per cent, second only to the internet, while in the first it had a positive reading of 1.8 per cent.