Mr Udy will start in his new position at the start of the 2025 school year.
The state-integrated co-educational Catholic school, which has about 450 pupils, was searching for a person to fill the position after Tara Quinney resigned in July.
Mr Udy’s fixed-term contract was ending, so he was searching for a senior leadership position.
"I have been in senior leadership roles for about nine or 10 years and in teaching for most of my life," Mr Udy said.
"I have worked in New Zealand, Australia and the UK, although I will say, I do enjoy New Zealand the most.
"St Peter’s College appealed to me because of its size, the fact that it’s co-ed and a Christian school.
"I have lived in provincial areas and tend to gravitate toward them for jobs, so St Peter’s felt like a perfect fit."
Mr Udy said he was looking forward to the role.
"It’s hard to say what it will be like, as I am not yet there, but I’m looking forward to getting to know the students and staff and ultimately forging a path ahead together."
Students were always at the centre of any school position and he was excited to lead the school as a principal, Mr Udy said.
"I am keen to learn more about the community and knowing how it works also."
St Peter’s College School Board presiding member John Hogue said they were "pleased" to announce Mr Udy as the principal.
"We were pleased to attract applications from high calibre candidates and are very pleased to announce that Mr Kieran Udy has been appointed."
"Mr Udy has experience as a Secondary School Principal. He was seconded to the role of Interim Principal at a Catholic primary school that was under statutory intervention, successfully assisting it to move back to full self-governance.
"Amongst a number of qualifications, Mr Udy has a Masters of Education (Hons) and a degree in Theology from the Sydney College of Divinity.
"We are very confident that Mr Udy will be a caring and committed leader of our whole school community."
"We know that the school and parish will make Mr Udy very welcome and look forward to having him join the Gore community. Mr Udy will be formally welcomed to the school with a mihi whakatau in the New Year."
