Last year the show plunged to its lowest listening figures since he took over the slot, dropping below five million in the third quarter of 2017, the first time in his five-year tenure.
The greatest amount of digital listening takes place on DAB radios - two-thirds of United Kingdom adults have access to one at home, and they are in 11m cars - which now accounts for 36.8% of all listening and 72% of digital listening.
Last year Norway became the first country to end national radio broadcasts on FM.
The new figures mean the government will nearly certainly consider a review of the future of FM radio soon.
The BBC said it would be "premature" to switch off the FM signal.
Mr Purnell said that BBC podcast listening was up a third across all audiences since the same time past year, accounting now for 40,000 hours a week.
"This is a landmark moment for for the radio industry and for listeners alike", said Ford Ennals, the chief executive of Digital Radio UK. "The digital transition is good news for radio and is helping our industry compete more effectively in the digital age".
Digital listening share is comprised of listening across all digital platforms - DAB in homes and in cars, Apps and online (which includes the growing number of smart and voice-controlled speakers) and DTV - and this is the first time that listening to digital has been greater than analogue platforms - FM and AM.
Digital has boosted the popularity of "live" radio.
The Radio 1 breakfast show has been defended by BBC bosses after figures showed it had shed hundreds of thousands of listeners since the start of the year.