Mr Cox arrived at St Philip's in 2009 when it was at South Cessnock, with 200 students.

He was appointed principal in 2014 - two years after the school moved to its current site at Nulkaba - and has seen it grow to 1250 students today, from prep to year 12.

Friday was Mr Cox's official last day, and he and his family will be moving to Sydney where he will take up a role as Head of School Design in the Catholic Schools head office.

The role will include designing brand new schools on greenfield sites, just as St Philip's was before it opened on Lomas Lane in 2012.

"I saw it as a chance to do something different - I have the experience and love of making schools engaging for learning," he said.

"It will be a bit different - the first time I haven't been based in a school, and the first time my kids won't have their Dad as the prinicipal."

Known as the man who puts the 'pal' in principal, Mr Cox said the 11 years he has spent at St Philip's have been the "most enjoyable time of his educational career".

"It has been incredible to watch this school grow, not only in the number of students, but to see our young people grow and flourish and thrive in their self-confidence, recognition and understanding of who they are," he said.

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The school has become nationally-recognised for its innovative programs and facilities, including its sports centre which was recently utilised by the Wallabies.

Mr Cox was named as a finalist in the Principal of the Year category at the Australian Education Awards in 2019, and just last month the school was named as one of The Educator's top 50 Innovative Schools in Australia.

"To see a school in Cessnock gain national recognition for what they're achieving in this town has been absolutely fantastic," Mr Cox said.

The new senior school building - which Mr Cox says is on par with any university - is due to open on the first day of 2021, and plans to build a 50-metre indoor pool are "still on the cards" as part of a bigger development application for the school site.

So why leave now, with such an exciting future ahead?

It's simply the right time to move on, Mr Cox says.

"The school is set and established now, it has excellent leaders, the staff are fantastic, and the culture is really positive," he said.

"I will always hold St Philip's Christian College dear in my heart.

"I know this school has got great days ahead of it."

Current deputy Matt Connett will be the acting principal until a new principal is appointed.

Mr Cox said Friday was an emotional day, saying farewell to the staff and families who have become good friends.

He said he and his family will be sad to leave Cessnock: "We love it here, we love the people and the town and the way they've embraced us, not just the school but the wider community.

"It's been an incredible journey."