Robinson, his voice breaking, told listeners at the end of Morning Report today that his last day would be on April 1 next year.
"I chose that date because it would be the report programme's 39th birthday, we started on the first of April, 1975.
"Apart from a couple of years reading the commercial news, I've been with the report programme all the way through.''
Geoff Robinson has announced on air his retirement from Morning Report. Thank you Geoff for your amazing contribution from all at MR & RNZ
"It also gives Radio New Zealand, I hope, plenty of time to find my replacement,'' Robinson said on-air, his voice cracking.
"This has been a complete surprise, Geoff did not let on about this at all so this is quite a shock,'' his co-host Simon Mercep said.
Robinson thanked his colleagues, Morning Report listeners and RNZ's chief executive Paul Thompson, who had suggested Robinson make the announcement himself.
"I'm not going straight away, I'll be here tomorrow, there'll be another programme and apart from taking a bit of annual leave before I go, I'll be here every day, all the way through to the first of April next year,'' Robinson said.
"It gives me a chance to thank my co-hosts, people like Simon. I actually once made a list of how many people I've worked with and I got to over 30, I must try and count it all up.''
Mercep returned his thanks to his co-host. "Most of us grew up listening to you Geoff.''
Robinson also thanked his family for "putting up with my very unsociable hours all that time''.
"And thank you, the listeners, for listening, my voice is cracking....there's more emotion here than I though there would be, so I'll try and control it.
"I do want to leave today with the usual words of saying, 'have a good day, talk to you tomorrow, here's the bird'.''
RNZ's Nine to Noon host Kathryn Ryan said Robinson shocked "everyone in this building'' with his announcement.
Ryan said there was a common theme to the tributes which followed his announcement.
"Which is, 'best wishes', shock, 'we love you', 'can't believe you're going' and lots and lots of praise along the lines of 'truly an intelligent, compassionate and thoughtful journalist'.''
Another tribute read, "I have a tear in my eye, what will we do without you,'' Ryan said.
"We'll just have to listen avidly until April.''
"Geoff, we will miss you desperately, bless you for the wisdom that you have brought us.'
