About 1.5 million viewers watch programmes on the internet each month, according to a study by research firm Colmar Brunton.
TVNZ head of emerging business Jason Paris said the broadcaster was among a limited number outside the US to embrace the concept, which it launched in 2007.
"I suppose it was a little bit of a leap of faith but we were reasonably confident it wasn't going to cannibalise our existing television audience and the research has shown it hasn't."
By "cannibalise", Mr Paris means viewers abandoning traditional habits to watch everything online.
But the Colmar Brunton research of 600 viewers showed more than 70% only watched OnDemand when they missed a show on TV.
TVNZ's next step will be to put first episodes of some shows online before they are broadcast.
"It won't be something we do for all shows," Mr Paris said.
"We'll pick particular shows that probably haven't played in New Zealand before and might be difficult to explain simply through a 30-second promotion or a billboard."
We'll give people the opportunity to watch the full episode so they can get into the show and understand what it's about before it's broadcast."
TV3's online programming is smaller, offering just eight shows of mainly New Zealand content.
Acting general manger Ande Macpherson said 50,000 viewers watched online each month.
There had been a 60% increase in traffic since January.
Ms Macpherson said the channel planned to expand its service, and was in talks with the relevant content owners. Alice Neville.
Most watched online
TVNZ
Shortland Street, Grey's Anatomy, Desperate Housewives, Gossip Girl, Coronation Street.
TV3
Outrageous Fortune, Underbelly, NZ's Next Top Model, Target, 60 Minutes.
