TVNZ director of content Jeff Latch said the show was nearing the end of its life cycle.
"TVNZ has chosen to focus its local content investment in prime-time programming. Good Morning has been a long-standing part of our schedule."
The show posted the news on Facebook and asked viewers to "stick with us" until its final episode.
"It's with great sadness that we advise Good Morning will be finishing up in December. It has been 19 years of fun and entertainment with some terrific people both in front of and behind the cameras. We'd really appreciate your support by sticking with us over the coming months - we hope to make it a celebration of our time on air. You will hear more from us on the show tomorrow."
About 15 people work on the programme on contract or as freelancers. Mr Latch said that where it was possible, TVNZ would provide opportunities for them in other parts of the company.
The magazine-style show, which began in 1996, initially ran for two hours and later three hours.
In recent years, the format changed, featuring news bulletins and moving to a one-hour format.
Nielsen ratings show the programme's popularity had waned this year, with an average audience of 54,000 viewers tuning in throughout August, compared to 64,000 in August 2014.