The record renewable share beat the previous best set in Q1, when renewables supplied 26.9% of the UK's electricity.
In the period of April to June, 45% of the renewable energy total was provided by wind capacity, 27% from onshore, and 18% from the UK's offshore wind projects.
"It's terrific to see that nearly a third of the UK's electricity is now being generated by renewables, with wind power leading the way," said RenewableUK executive director Emma Pinchbeck.
"Onshore wind performed particularly well, with generation increasing by 50% compared to the same period last year.
"When the Government holds the next set of competitive auctions for contracts to generate electricity, low-cost onshore wind deserves the chance to compete," Pinchbeck added.
According to Windpower Intelligence, the research and data division of Windpower Monthly, the UK's wind capacity grew from 14.7GW at the start of April to 15.5GW at the end of June.