The Lions almost inflicted a series defeat on the All Black after splitting the three-game matchup 1-1 with the world champions in New Zealand in July.
Gatland oversaw a memorable Second-Test victory for the Lions, who ended New Zealand's 47-game winning streak at home.
However, New Zealander Gatland was criticised in his homeland and by his own Lions players – namely flanker Sean O'Brien – leading to his exit.