The England forward ended the Foxes’ Premier League goal drought and secured a 3-1 win – their first since New Year’s Eve – to lift the hosts out of the relegation zone, four days after the departure of title-winning manager Ranieri.
Danny Drinkwater netted a brilliant second goal between Vardy’s strikes, with Philippe Coutinho’s effort midway through the second half scant consolation for the lacklustre Reds.
Caretaker manager Craig Shakespeare and his team made light work of the controversy and speculation which had surrounded the club in the build-up to the match.
Vardy had been one of the players named as having reportedly met with the Thai owners to discuss Ranieri’s future – an accusation he fiercely denied – and there was clear anger and frustration in his display.
Liverpool – who missed the chance to return to the top four – were completely unprepared for the revived champions, who demonstrated more effort and energy than they had for weeks in the league.
Shakespeare trusted the team which virtually picked itself to win the league last season, apart from Wilfred Ndidi replacing the departed N’Golo Kante.
It was a sad indictment of the Foxes’ summer transfer business, with just two of their pre-season signings in the squad and £16million Ahmed Musa dropped completely.
But the old guard responded, which surely would have left Ranieri wondering where that commitment had been following just five previous league wins this term.
There was no vitriol from the supporters as Leicester went at Liverpool having dropped into the bottom three over the weekend.
Vardy was lucky to escape punishment after catching Sadio Mane on the ankle as the home team signalled their robust and determined intent early on.
The Foxes had rarely been so energetic this season and Simon Mignolet made two smart saves from Robert Huth and Shinji Okazaki before the visitors even got into the Leicester box.
When they did, Wes Morgan denied Joel Matip a tap-in by scrambling away Mane’s cross and the hosts’ momentum subsided as the Reds began to see more of the ball.
But they needed Mignolet to bail them out after 19 minutes when Lucas Leiva made hash a of Kasper Schmeichel’s clearance, only for Vardy to miscue and Mignolet saved with his legs.
Yet there was no stopping the England striker, in front of the watching Gareth Southgate, nine minutes later when he put Leicester ahead with their first league goal of 2017 and first in 637 minutes.
Liverpool failed to get hold of the ball in midfield and Marc Albrighton instantly split the visitors’ defence with a first-time ball to put Vardy clean through.
He easily slotted past Mignolet for his first Premier League goal in almost three months in a throwback to last season, when he thrived on such service.
The revived Foxes continued to press – although they needed Schmeichel to save at Coutinho’s feet – and doubled their lead six minutes before the break thanks to Drinkwater’s excellent strike.
James Milner could only half-clear Albrighton’s cross to the England midfielder and, 25 yards out, he unleashed a stunning half volley into the corner.
Schmeichel still needed to save Emre Can’s bouncing attempt before half-time and Liverpool toiled with the ball but never threatened Schmeichel after the break before Vardy sealed the game on the hour mark.
Neat play from Riyad Mahrez and Christian Fuchs saw the latter flummox Adam Lallana and cross for Vardy to power in a header from close range.
Liverpool still had some fight left and Schmeichel saved from Lallana before Coutinho pulled a goal back with a fine low finish with 22 minutes left, but it was all too late.
Drinkwater and Lucas traded half chances and Schmeichel almost spilled Coutinho’s late effort, but Leicester’s post-Ranieri era began with an impressive victory.