He has several Rugby World Cups, Commonwealth Games and many other important test matches under his belt.
However, he confessed there was a different feeling working at an Olympics.
O’Brien has been the sevens referees high performance manager since the sport was admitted into the Olympics in 2016.
Now, he is once again gearing up to be part of the international event.
"I'm really excited. I've been involved in five Rugby World Cups and three Olympics — the Olympics was always a special one.
"There is something about it. For me, it's the greatest competition you can go to."
O’Brien will be responsible for the 23 referees appointed to the competition.
"They come from 14 different countries and include Nick Hogan and Maggie Cogger-Orr from New Zealand."
"The camp is mainly to focus on what we call the key areas for refereeing — the key elements of the breakdown, advantage, and foul play. The referees also do their fitness training.
"It is just a time that we try to come together for morale."
After the camp in Portugal, the crew will fly to Paris.
The men’s competition starts on July 24 — three days before the opening ceremony.
Nearly 100 boats will parade down a 6km stretch of the Seine, passing by some of the city's iconic bridges and landmarks — including Notre-Dame and the Louvre — and
Olympic venues.
To be able to see this event in the flesh will be the highlight, he said.
"It will be great because this year it is a very different one with athletes travelling through the river [Seine], so I am looking forward to that."
O’Brien will be in France until the end of the women’s competition on July 30 and travels home the next day.
"I think it will be really nice to be part of such an event and then watch the rest from my couch.
"The Olympics is the pinnacle event for all referees, including me."
