Plunket has co-hosted Morning Report since September 1996 and has won numerous media awards for his work.
Radio NZ head of news Don Rood said today it was with great regret that he announced Plunket's resignation.
His last day at RNZ will be September 8.
Morning Report enjoyed ratings success as the country's most popular breakfast radio show, Rood said.
Plunket had been a big part of that success.
"I wish him all the best."
Plunket had threatened to resign a number of times in the past.
His latest run in with Radio NZ went through the Employment Relations Authority, where the broadcaster won a ruling allowing it to ban Plunket from writing the political column while on the public payroll.
Plunket confirmed at the weekend that he had reached an agreement with RNZ and his first political column would appear in next month's Metro magazine, the Herald on Sunday reported.
Metro editor Simon Wilson said Plunket would be "writing from within the Wellington political scene".
Plunket has also worked in television, including stints on Fair Go, a number of years as TV3 political correspondent in the press gallery and with current affairs show Holmes.
