The New Zealander said: "I have really enjoyed working with Joe (Schmidt), Les (Kiss) and the players over the last few months. But, at the end of the day, family must come first and we must do what we think is best for the Plumtree family.
"I would like to thank the IRFU for their understanding and wish everyone involved in Irish rugby the best of luck for the future."
Ireland team manager Michael Kearney commented: "The Ireland squad and management team would like to thank John for his contribution to the team's success over the past season.
"We are sad to see him go but our best wishes are with John and his family on their return to New Zealand."