The former Scotland international will be joined by John Collins, who also becomes part of the Scottish FA performance department to assist part-time with the national youth team.
Gemmill has previously helped the Scotland U19 and U21 squads on a game-by-game basis but has now been employed full-time with the U15, U16 and U17 Scotland squads, where he will work alongside Scott Booth.
Gemmill played 26 times for his country in a career that included spells with Nottingham Forest, Everton, Preston North End, Leicester City, Oxford United and New Zealand Knights.
"I have been working alongside Billy Stark, Ricky Sbragia and Scott Booth with the national youth teams for some time now and am delighted to be joining the international set-up on a full-time basis," he told the SFA's official website.
"Mark Wotte (Scottish FA Performance Director) has shown great faith in my abilities and I can't wait to contribute to the Scottish FA's Performance Strategy in this new full-time role."
Wotte was pleased with the confirmation of Gemmill's new role and also welcomed former Hibernian and Celtic midfielder Collins, who scored 12 goals in 58 appearances for Scotland.
"Scot impressed us hugely when he undertook his UEFA Pro Licence coaching course recently," he said.
"He has a wealth of experience from playing and coaching in the Scotland international set-up and I am delighted he has accepted the offer of joining us on a full-time basis.
"John was a terrific player for Scotland and has great experience as a coach. I am sure having Scot and John on board with the national youth teams will be a great boost to our many talented young players."