Friends and family from Canada, Los Angeles, the UK and Germany attended.
Mr O'Brien described the ceremony as possibly the shortest on record but said the celebrations continued into the early hours of the morning.
The British writer and actor said he and Ms Graf, originally from Bavaria, Germany, met through the London theatre scene more than 10 years ago and had been dating for three years.
The couple got engaged last year while O'Brien was working on Hamilton Operatic Society's version of Oliver!
"I asked Sabrina to marry me on our last night.
"She came over for the last night. Mark Sainsbury drove her down. I caught her when she was jet-lagged. Thankfully she said 'yes'."
Mr O'Brien has spent several years travelling between the UK and his Katikati home "but we've come out for good now".
"We are going to put down our roots," he said.
Mark Sainsbury and Mr O'Brien have been friends since they met in London in the mid-1990s while Mr Sainsbury was a Europe correspondent.
Mr Sainsbury said the couple adored each other and he was more than happy to help Mr O'Brien propose.
"I didn't say anything of course but I picked her up [from the airport]. He had been talking about the fact that he'd been thinking more and more about it."
Mr Sainsbury said he was proud to have Mr O'Brien as a friend and was prouder still to celebrate his wedding to Ms Graf.
"He's a pretty unique character, Richard, but I think he wants to try to keep it nice and private and romantic," Mr Sainsbury said.
Mr O'Brien is well known for cross-dressing and in an interview with BBC Radio 4, said he felt he was about 70 per cent male, 30 per cent female.
In December 2011, Mr O'Brien was granted New Zealand citizenship after deciding to retire in the Bay of Plenty.
Mr O'Brien was raised in Tauranga when his English father went to New Zealand to become a sheep farmer in 1952.
He spent his teens and early 20s in Tauranga and Hamilton, before leaving for the UK in 1964.
