The news came as a Monday night draw put second-placed Tottenham out of mathematical contention to raise one of football's biggest prizes, and the social media storm erupted.
Football luminaries past and present announced their delight with the win, with Leicester legend and hometown boy Gary Lineker leading the plaudits -- a far cry from his dismissive "Claudio Ranieri? Really?" tweet of last summer.
Lineker sent out a tongue-in-cheek update via Instagram, claiming an error with his previous tweet, claiming that it "was sent prematurely. Meant to say 'Claudio Ranieri? Really really brilliant!'"
Even Tottenham (another of Lineker's former clubs), which saw its title challenge evaporate following its 2-2- draw with last season's champion Chelsea, recognized the magnitude of the achievement and responded with magnanimity.
The Twitter UK bot dutifully pointed to a huge spike in traffic as the final whistle blew between Monday's London derby between Spurs and Chelsea, handing the title to the Foxes.
Meanwhile, tweeters up and down the country put aside geographical and team rivalry to congratulate Leicester and the team's fans -- while the improbability of the achievement resonated with football romantics in the UK and further afield.
User Jake Humphrey compared the title triumph to the football video game "Championship Manager," where players simulate seasons with their favorite teams, with the aim of finally providing the fairytale ending that so many fans hope for.
"You wake up to the fact that Football Manager is now something that happens in real life," he writes.
Optimism was running high, with one user using the occasion to place the champion-elect in the same category as serial Spanish title-winner Real Madrid -- as long as you set the parameters correctly.
"Last 8 years: Real Madrid - 1 league title; Leicester City - 1 league title. Amazing," @FootballFunnys wrote.
For some, it was an opportunity to clear up one of the biggest mysteries of the year: The "greatest service Foxes have done for their city is now the world knows how to pronounce Leicester," said user Khairy Jamaluddin.
But others admitted that it was still beyond them, with Luke Carrell taking the opportunity, while "the Brits are asleep," to own up that the "pronunciation of Leicester" is still "baffling" to him.
For many around the world, especially fans in Thailand -- where the club's owners are based -- and Japan, where striker Shinji Okazaki hails from, the news came in the middle of the night. Nonetheless, there was an outpouring of support from far-flung football fans.
"You don't have to be a fan of Leicester to be crying tears of joy today," said Hargu-san, who appeared to have taken the Twitter handle @hargreeeeaves from former Bayern Munich and Manchester United player Owen Hargreaves.
It was the culmination of eight months of hard work and an amazing reserve of self-belief. ESPN sports business reporter Darren Rovell remembered a moment two months ago, when it became increasingly apparent that the title challenge was no mirage. His video of Leicester fans singing "We're gonna win the league" was vindicated late Monday night.
But there were moments of regret, however tangential. A self-proclaimed Liverpool fan tweeted that he wished he "could go back in time, tell myself to bet on #Leicester title, problem is, I wouldn't have believed myself."