The outcome is likely to pile more pressure on Magpies manager Rafa Benitez and worsen still further his relationship with the board, as his team look destined to face another tough relegation battle, with the squad lacking any bite up front while conceding soft goals at the other end.
Leicester, who moved up two places to seventh, with 12 points, always looked more likely to score as Ricardo Pereira forced a good save from Newcastle keeper Martin Dubravka with a low shot in the 10th minute.
Mohamed Diame missed with a free header for the home side midway through the first half, and that turned out to be their best chance on a frustrating afternoon.
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Leicester continued to dominate and the lively Vardy fired them ahead with a 30th-minute penalty after DeAndre Yedlin needlessly blocked Maguire's wayward volley with his arms amid a penalty-box scramble.
The home side's final pass continued to go astray in the second half as they failed to create any chances, and England defender Maguire sealed Leicester's victory when he headed home a James Maddison corner in the 73rd minute.
Maguire and Leicester manager Claude Puel heaped praise on 21-year old midfielder Maddison, who has hit the ground running at Leicester after his close-season move from Championship side Norwich City.
"James Maddison continues to give his best and improve," Puel told the BBC."He has to continue that work and we will see in the future."
Maguire added: "Maddison takes all the set plays now so we look dangerous.
"He's definitely good enough to play for England. It's a matter of time. If he keeps improving he'll get the call and he will take the challenge on."
(Writing by Zoran Milosavljevic; Editing by Clare Fallon, Neville Dalton)
