However, this will be the first time he will be the key man on the field.
Long-time friend and fellow football referee Brett Chibnall said O'Leary has been preparing for months for the big event.
"He's done an awful lot of work. He's extremely fit and knows his job extremely well. He's put a huge amount of time and energy into [preparations]."
Mr Chibnall said his friend had hardly been in touch over the past few weeks because of strict conditions of the tournament.
He said he was not surprised by O'Leary being announced as a ref, as he was highly regarded and considered one of the best referees in the Oceania region.
"He's very hard working and a dedicated person."
O'Leary has been a referee for between 15 to 20 years and has appeared on football pitches in Wellington, Waikato and now further north, in and around Whangarei, where he lives with his wife and children.
He is a former student of St John's College in Hamilton where his passion for refereeing started.
Mr Chibnall said: "He played for a little while and then realised he wasn't a very good player, so took up refereeing and worked hard on [that].
The Waikato and Bay of Plenty Football group - which O'Leary was heavily involved with for many years - was also proud of their former colleague's achievement.
Mark Ball, who oversees referees in the Waikato region, said O'Leary had always been a well-regarded ref who was committed to being fair on the pitch.
"Peter is clean-cut and a very cool, calm and collected ref. It's a good example to up and coming refs here in New Zealand - that this is where you can get up to."
The match that O'Leary will oversee tomorrow is a crucial one for both teams, who will need a win to boost their chances of moving on in the tournament.
He will also be joined by fellow Kiwis Jan Hendrik Hintz and Mark Rule as assistant referees.
O'Leary has accumulated the most participations (five between 2007 and 2012) and refereed the most matches (five) in the Fifa Club World Cup.
He has also taken part in four editions of the Fifa U-20 World Cup from 2007 to 2013.
Peter O'Leary's moment on the world stage screens from 10am tomorrow.