The Scottish centre-back also penned a new contract with the Magpies prior to making the switch to Brunton Park.
McArthur, who has featured 15 times at under-21 level this season, joined from Kilmarnock in the summer of 2022 and captained his country during Scotland’s 2024 European Under-19s Championship qualifiers.
The defender now joins a Carlisle side managed by former Magpie Mike Williamson and will also link up with Paul Dummett, who has recently joined the Cumbrians.
Everyone at the club wishes Charlie well for the remainder of the campaign.