The Dunedin-born 54-year-old is not due to take over from present principal Mike Corkery until January next year, and he said it would be inappropriate to reveal his hand until after Mr Corkery's departure.
Mr Garry is the college's deputy principal, and has taught at the school since 1986, during which time he has been head of several departments, the boarding hostel manager, assistant principal (1997-2001) and deputy principal since 2001.
John McGlashan College Board of Trustees chairman Barry Kelk said Mr Garry was chosen after a ''thorough and exhaustive'' selection process over several months, from which he clearly stood out as a leader and educator.
Mr Kelk said there were 15 applicants for the position, from throughout New Zealand and several from Australia, and he was impressed with the calibre of those who applied.
''Mr Garry has the unanimous support of his new employer, the board of trustees, and we are confident he has the skills, ability and leadership qualities to preserve, then grow, the performance of what is one of New Zealand's leading boys' secondary schools.''
College Board of Proprietors chairman Keith McArley welcomed the appointment, believing Mr Garry would preserve and enhance the school's special character as it prepared to celebrate its centenary in 2018.
Mr Garry said he was delighted and excited about his new role at the college.
''I feel very lucky to have this opportunity. It's a very special place; it's uplifting.''
He was looking forward to beginning his new role, continuing the high standard of education, and doing the best he could for every boy at the school, ''no matter who they are''.
In announcing Mr Garry's appointment, both Mr Kelk and Mr McArley praised Mr Corkery's 18-and-a-half-year contribution to the college.
Mr Kelk said Mr Corkery inspired the construction of the Edgar Learning Centre, which was widely respected as an innovative teaching and pupil area, and it was a testament to his innovative approach to education.
''Mike has been an inspirational leader and an outstanding educator who has helped make John McGlashan College a leading school, both in the educational achievements of its students and the quality of the men who graduate.''
