Over the same period, Newstalk ZB's audience has risen from its previous cumulative weekly reach of 598,400 listeners.
GFK releases the commercial and non-commercial stations separately to draw a distinction between the entities.
Commercial stations rely on advertising to fund their broadcasts, while RNZ is supported through Government funding.
Newstalk ZB has long been the top commercial talk station in the country, but this marks the first time that the station overtakes non-commercial RNZ.
While RNZ doesn't compete with Newstalk ZB for advertising dollars, critics have long pointed out that Newstalk ZB's claim of supremacy would always have an asterisk due to the size of RNZ's audience.
However, it wasn't all bad news for RNZ.
The broadcaster's Concert station saw its weekly listenership rise from 218,300 in the previous survey to 229,500 this time.
Concert was at the centre of much controversy last year, when plans were revealed to scale back the station and remove it from its FM slot.
A public outcry, which also included the powerful voice of former Prime Minister Helen Clark, saw the changes scrapped by the broadcaster.
Beyond the continuous competition for the coveted number one slots across segments, the overall figures told a good story for the radio industry.
The data showed that more than 3.7 million New Zealanders continue to listen to the radio every week and almost 3.5 million of those listen to commercial radio stations.
The continued relevance of radio was reiterated in 2020 by significant spikes in the number of people tuning in to stations around the country.
But this growth in audience wasn't always matched by a corresponding commercial lift, with 2020 seeing a decline of around 15 per cent in radio revenue.
"There is some irony in this for the industry as more and more New Zealanders of all ages turned to radio for trusted news, information, music and entertainment with most stations seeing cume [overall weekly reach] increases from the same time last year," said Jana Rangooni, the chief executive of the Radio Broadcasters Association.
With the advertising market showing signs of a swift recovery in 2021, most of that revenue does look likely to return to the radio industry this year provided the nation isn't hit by another wave of Covid.