The Magpies' all-time longest-serving former player, who made 199 appearances in 20 years at St. James' Park, gained his coaching badges at the Irish FA and has linked up with Northern Ireland manager Michael O'Neill - himself an ex-Newcastle player.
But he will also continue to work full time with Newcastle's young goalkeepers, and will travel to Woking with Ben Dawson's under-23s for Friday night's Premier League Cup clash against Reading before meeting up with the Northern Ireland squad ahead of their European Championship qualifiers against Estonia and Belarus.
"The national team role is part time and Michael O'Neill was very keen to get people who are in it day in, day out so at the international camps we are sharp and fresh and ready for what is the ultimate level of football," Harper told nufc.co.uk.
"I'm delighted. It's been a bit of a whirlwind, to be honest. Since finishing my Masters (in Sport Directorship), there have been a lot of offers coming in to me but this one was something I found particularly attractive.
"I met Michael O'Neill at a Newcastle game about six weeks ago and we were just talking football - nothing was mentioned about any roles, it was just a general chit-chat about Newcastle United. Michael obviously played there back in the day and it was the first time I'd met him.
"Then I got a call out of the blue just to say that the position was available and would I be interested in doing it? The opportunity to work at international level was something I wasn't fortunate enough to do as a player but I have a lot of European experience from my time at Newcastle and, briefly, at Hull, and it's an opportunity you can't afford to turn down.
"I have to thank Newcastle for their support in the matter; Lee Charnley, Joe Joyce, Ben Dawson and Simon Smith were all very supportive.
"During international breaks, we have goalkeepers away as well, which helps manage the situation in my absence, and we have some very good goalkeeping staff, with a bigger pool of staff now.
"It's great and I can't wait to get started but we've got an important under-23s game in the Premier League Cup on Friday that I'm fully focused on. Then, as of Sunday, when I go away, I'm looking forward to meeting the rest of the staff and the players ahead of two big games."
Michael McGovern, Bailey Peacock-Farrell and Conor Hazard are the three goalkeepers named in O'Neill's latest squad and Harper said: "Bailey Peacock-Farrell has had a lot football at Leeds, certainly in the early part of the season, and I'm going to watch young Conor Hazard - who is on loan at Partick Thistle from Celtic - at Hearts tonight.
"Michael McGovern, who has done an excellent job and had a fantastic Euros (in 2016) is down at Norwich with Tim Krul, and Trevor Carson, who has played the last few internationals, is out at the minute (through illness). I'll be speaking to the staff at the younger age groups with an eye on what's coming through, as well.
"I completed my UEFA A Licence and have just completed my UEFA Goalkeeping A Licence with the Irish FA over in Belfast, and I've ben very, very impressed by the staff and the support from the likes of Alan Walker, Nigel Best, Tommy Johnson, who's a Geordie lad, and more recently Packie Bonner on the UEFA goalkeeping course."
United's under-23s were beaten 3-0 by their Aston Villa counterparts on Monday night, having been knocked out of the Northumberland Senior Cup at the semi-final stage by Morpeth Town last week. But they remain fifth in Premier League 2 division two and have kept clean sheets in three of their last four league outings.
"I'm big on team clean sheets," Harper insisted. "John Burridge - my first very goalkeeping coach - used to tell me they're a 'goalkeeper's hat-trick' but we're very big on goalkeepers now being seen as part of the team and getting more involved in team practices, so clean sheets are very much a result of a team performance.
"As much as the last week has been disappointing, we've still got the Premier League Cup, we've still got the play-offs to go for, and in football you have a lot of ups and downs so it's important not to get too focused on a disappointing week and remember a lot of the excellent stuff that's gone beforehand.
"The focus now is Friday. We have good memories - we beat Reading down there a few weeks ago and hopefully we can go and do the same again before the focus switches back to the league."
