Stephen Frail was previously on the coaching staff at Celtic and Hearts
Stephen Frail says renewing a partnership with Micky Mellon inspired his decision to leave the Northern Ireland set-up and become assistant manager of Dundee United.
United have confirmed the appointment two days after he stood down as national Under-17 and Under-19 manager.
Frail and the new United manager were team-mates at Tranmere Rovers.
"Micky and I have known each other for over 20 years - when I got his call, I had no hesitation," Frail said.
"I also wanted to get back into working with senior players every single day."
Frail, who took over the joint roles for the Irish FA in 2016, formerly coached with Celtic and Hearts.
"I'm really excited to be joining a very big club who have got great ambitions to do well in the Scottish Premiership," Frail said.
"Hopefully, we can improve on everything that has already been done here and have a successful season."
With Ian Baraclough having been promoted to take over as senior Northern Ireland manager, the Irish FA now have vacancies for their under-17, under-19 and under-21 posts.
Baraclough praised Frail's input to Northern Ireland football during his time with the Irish FA.
"He has been a real asset for the development of our underage groups and the association as a whole," said the new Northern Ireland manager.
"He joined on my first trip as the U21s manager to Estonia and was a huge help to me during that period."
The Uefa European Under-19 Championship finals had been due to take place in Northern Ireland in July but were postponed because of the ongoing coronavirus pandemic.
