McArthur is Newcastle’s sixth summer arrival in total after youngster Alex Murphy from Galway United, Matt Targett from Aston Villa, Nick Pope from Burnley, Sven Botman from Lille and former Tottenham Hotspur academy player Jordan Hackett.
McArthur is expected to join up with the club’s under-23s side ahead of the new Premier League 2 Division 2 season.
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Who is Charlie McArthur and why did Newcastle United sign him?
McArthur, who turned 17 in May, has been lauded as one of the brightest young prospects in Scottish football having captained his country at under-17s level and also breaking into Kilmarnock’s first team. He appeared four times for the Scottish Championship winners last season.
Due to his potential, the 6ft 2in central-defender has attracted interest from several other Premier League clubs including Manchester City, Liverpool, Brighton, West Ham and Wolves with a £275,000 bid previously reported.
While Newcastle are actively looking to strengthen their first team squad this summer, they are also planning for the future and looking to establish a competitive academy set-up.
Newcastle’s under-18s side finished bottom of the league last season while the under-23s failed to make the play-offs in the Premier League 2 Division 2.
What Charlie McArthur has said about his future
In May, McArthur said: "I'll speak to the manager when I get back [from the Under-17 Euros] and see what the plans are and go from there. I'm still under contract for another year so I am still a Kilmarnock player.
"Derek McInnes has been good to work for. I'll just need to see what happens when I go back and it'll all work out.
"It's not difficult to focus despite the speculation because at this moment in time I'm not playing in England.
"It was brilliant to make my league debut for Kilmarnock at Raith Rovers a few weeks ago. It's been great around the club.
"The players have all been buzzing. We are a good group and everyone can't wait to play in the [Scottish] Premier League next season.”