His coaching ability was recognised in 2017 when has was appointed head coach of the New Zealand Provincial Barbarians side who faced the British and Irish Lions during their 2017 tour of New Zealand and was announced as head coach of the Māori All Blacks that same year.
Chiefs Rugby Club CEO Michael Collins commended McMillan on his appointment.
"We are excited for Clayton to lead the Chiefs in 2021. He is a talented coach and was a stand-out candidate. He boasts an excellent track record of developing players and delivering success.
Not only during his tenure as the director of rugby for the Bay of Plenty Rugby Union, but during the Māori All Blacks and New Zealand Provincial Barbarians campaigns. The results he has achieved reflects his leadership ability."
"Clayton is no stranger to the Chiefs team, having already worked alongside assistant coaches Roger Randle and David Hill and a number of the Chiefs playing group," said Collins.
McMillan said he was grateful for the chance to lead the Chiefs.
"Super Rugby has certainly been a goal of mine and I am honoured to be appointed as the interim head coach for the Gallagher Chiefs. There is a fantastic pool of gifted athletes to work with along with an experienced and talented management group."
When Gatland was appointed Chiefs coach he had already agreed to lead the Lions to South Africa in 2021.
