The 23-year-old striker has not started a game for Gladbach since April of last year and has fallen way down the pecking order at Borussia Park.
Newcastle tried to sign De Jong from Twente in 2012 but it was the Bundesliga club who won the battle for his signature when they paid over £12million.
Newcastle have kept tabs on De Jong's situation and opened talks with Gladbach in December - and now a deal has finally been agreed.
Borussia announced via their Twitter account that De Jong was no longer training with them and was set to travel to England.
De Jong, who still hopes to make the World Cup with the Netherlands, will have his Magpies medical during the next 24 hours and could join on loan with a view to a permanent deal in the summer.
The news came as France midfielder Yohan Cabaye prepared to undergo his medical after the Magpies agreed in principle to sell him to Paris Saint-Germain on Monday evening.
Alan Pardew has been desperate to strengthen his striking resources during the current window with Loic Remy only on loan, Shola Ameobi out of contract at the end of the season and Papiss Cisse having been repeatedly linked with a move away from the club this month.
Indeed, it was previously mooted that a swap deal involving Cisse and De Jong could be arranged, although that was dismissed by Newcastle. Pardew insisted on Monday that he did not expect Cisse to leave the club this week.
Should the deal go through, De Jong's first involvement could come in Saturday lunchtime's Tyne-Wear derby clash at home to Sunderland.