Harding, 24, a virtual ever-present for the club in the Championship since joining from Birmingham City in the close season will be part of the Reggae Boyz squad who travel to Austria to face the USA in an international friendly on March 25.
Millers’ colleague Curtis Tilt - who is currently on loan at League One club Wigan Athletic - is also in the party after his first call-up - alongside fellow English-based players Amari Bell, Ethan Pinnock, Liam Moore and Andre Gray.
While in an ideal situation, Warne admits that he would to keep his squad all together and not have to worry about any players getting potential injuries on international break, his delight at Harding’s elevation surpasses that feeling.
“He said: It's difficult being a manager. I want what's right for the players first and foremost. However, my job is to focus on what's best for the football club.
It's a bit ying and yang. But I'm always pushed by the player. I'm just really pleased for him.
"He's a really, really proud young man anyway. When I signed him, half of his family came, which I thoroughly enjoyed. I was speaking to his dad and brother-in-law.
“I know how much he is part of a big, loving family and I know how much his call-up will mean to all of them. It can't but help him as a player.
“I appreciate there's a lot of travelling and he might come back a bit fatigued, but once that first game is out of the way I might have an even better player on my hands.
“His call-up is testament to the great season he's had. I'm really proud of him and sincerely pleased for him.”