Board of trustees chairman Richard Wingham said Mr McIvor would take over leadership of the school at the start of term 3.
Mr Reddiex left the school last week to become rector at Dilworth School in Auckland.
Former Wellington College headmaster Roger Moses will be acting rector in term 2.
Mr Wingham said the board was impressed with the calibre of applications for the permanent role and was delighted to secure Mr McIvor as the new rector.
He said Mr McIvor had been the rector of Timaru Boys' for the past five years and had led the school through a period of change and consolidation, positioning it for continued success.
''With 24 years of experience in education - 16 of these specialising in boys' education - Mr McIvor has demonstrated a passion for boys' education and a clear understanding of the King's culture of personal excellence.
''Mr McIvor brings significant boys' school experience, combined with traditional values that are essential in maintaining the culture and high performance of the school.''
Mr McIvor has also been deputy principal at Avondale College, Auckland, and has also taught at Auckland Grammar School (social sciences) and Derby Grammar School, in England.
He has a master of business administration degree (MBA), with distinction, from Massey University and a BA (Hons) from the University of Canterbury.
