Goals from Jonjo Shelvey and Ayoze Perez now have Rafael Benitez's resolute side on the brink of top-flight safety after three straight successes, denting Leicester's hopes of European qualification in the process.
Newcastle have not typically fared well at the King Power Stadium, failing to taste victory in their only five prior visits – including Benitez's first game in charge in 2016 – and scoring just once.
But Saturday's clash was a decidedly happier affair for the visiting supporters as Shelvey – tipped for an England call-up by his manager – struck his first Premier League goal for the club before the Magpies dug deep in an all-action defensive display.
Perez, who netted an own goal in the reverse fixture, added a bizarre second to take Newcastle within just two points short of Benitez's 40-point target and up to 10th with six games remaining, despite a late Jamie Vardy goal.
Newcastle started brightly and Kasper Schmeichel was forced into an early stop from Perez's flicked header, comfortably claiming a second Dwight Gayle effort shortly afterwards.
And the opener deservedly arrived after 18 minutes. Perez led a counter-attack and picked out Shelvey in the middle, who sold two defenders with a dummy before coolly placing a shot into the bottom-right corner.
Harry Maguire was perhaps then fortunate to escape with a yellow card as he appeared to aggressively shove Gayle in the face, the pressure rising as players from either side went head to head.
Fousseni Diabate dragged well wide after a lovely piece of skill created a rare Leicester opening, before the home crowd reacted with fury as referee Stuart Atwell deemed Paul Dummett to have pulled out of a challenge with Riyad Mahrez just in time inside the area.
Leicester ended the first half on top and, although Gayle then sent a free-kick dipping just over the top, that continued after the restart.
But the Foxes failed to trouble visiting goalkeeper Martin Dubravka and they were undone a second time when Florian Lejeune's long ball bounced between Maguire and Wes Morgan, allowing Perez to nip in and lob Schmeichel.
The home side belatedly rallied in the final 10 minutes, however, and Vardy pounced a yard from goal to toe Shinji Okazaki's header across the line, setting up a nervy finish but not one on which Leicester could capitalise.
Key Opta facts:
- Newcastle United recorded their first victory at the King Power Stadium in all competitions, having previously lost three and drawn two.
- Leicester City lost for the first time in seven home Premier League games, since a 3-0 defeat to Crystal Palace in December (W2 D4).
- Newcastle have won three consecutive Premier League games or the first time since September.
- Ayoze Perez both scored and assisted in a single Premier League game for just the third time in his career and first since October 2015 vs Norwich City.