Barnet cross-communal secondary school JCoSS is endeavouring to have a new headteacher in place for the September academic year following the resignation of Jeremy Stowe-Lindner.
Mr Stowe-Lindner - who was instrumental in the successful launch of JCoSS in 2010 and its subsequent development - will leave in the summer to become principal of Melbourne's Bialik College, another cross-communal school.
He said the decision to move to Australia, where his extended family lives, had been taken only after much soul-searching.
"I could have stayed at JCoSS for my entire career and truly feel that I have the best job in the community.
"But after a great deal of thought, I felt that the offer of a principalship in a similar cross-communal school in Melbourne, close to our children's grandparents, was an opportunity we had to take."
He would miss the "wonderful" JCoSS students and "my passionate and dedicated colleagues".
Thanking Mr Stowe-Lindner for his "outstanding contribution", governors' chair Mike Grabiner added: "The governing body will be undertaking a thorough recruitment process to find a new headteacher. We will select somebody with the determination, drive, skills and enthusiasm to lead our school." They also wanted someone with "a strong commitment" to the JCoSS ethos.
The school has 344 pupils in years seven and eight. Another 187 will join in September, plus up to 40 in its new sixth-form.