Warner, 43, joins head coach John Gregory's coaching staff which already includes assistant coaches Mark Lillis and Syed Sabir Pasha and sports scientist Niall Clark.
The former goalkeeper had a playing career spanning more than two decades with the majority of it having spent in English football.
He has had spells at Liverpol, Hull City and Fulham and played over 200 league games for Millwall, having also reached the FA Cup final with them in 2004.He also represented Trinidad and Tobago at international level.
"I am delighted to have joined Chennaiyin's coaching staff and grateful to the club and John Gregory for giving me this opportunity. I have already enjoyed working with the keepers here and look forward to help them develop and have a great season ahead," Warner said from Chennaiyin's pre-season training base in Hua Hin, Thailand.