Both Hussey and Mills will work under former New Zealand wicket-keeper batsman Brendon McCullum, who has been appointed as the head coach of KKR for the next IPL.
"It's great to welcome David Hussey and Kyle Mills to the Kolkata Knight Riders family. They bring a wealth of experience as professionals and are terrific individuals," KKR CEO and Managing Director Venky Mysore said in a statement.
"We are confident that their contribution as part of the think tank of KKR and to the KKR academy will be invaluable."
The 42-year-old Hussey, who has played over 300 T20 matches across franchise and international cricket, was part of the KKR team from 2008 to 2010 as a player.
Mills, 40, ended his playing career in 2015 as New Zealand's second highest wicket-taker in ODIs with 240 wickets from 170 matches.