The internet star and "dad blogger", real name Mark Hoyle, fended off competition from artists including Stormzy, Lewis Capaldi and Dua Lipa to take the festive accolade with his charity single I Love Sausage Rolls.
The song is a twist on I Love Rock 'n' Roll by Joan Jett and follows in the footsteps of his 2018 Christmas number one We Built This City, an ode to sausage rolls parodying Starship's classic hit.
I Love Sausage Rolls scored 93,000 chart sales over the past week, selling 18,000 copies more than his 2018 release, the Official Charts Company said.
The vlogger's success means he is the first artist to score consecutive Christmas number ones in more than 20 years.
The Spice Girls are the last to achieve the feat, scoring three in a row in 1996 to 1998 with their hits 2 Become 1, Too Much and Goodbye.
All proceeds for the novelty song go to food bank charity The Trussell Trust for the second year running.
LadBaby told OfficialCharts.com: "How have we done this again? It's the best feeling in the world - it's a Christmas miracle yet again!
"Thank you everybody for supporting us once again, and all for an amazing cause. It's going to the Trussell Trust - to the 14 million people living in poverty in the UK. Who doesn't love a sausage roll at Christmas?"
Martin Talbot, chief executive of the Official Charts Company, said: "Congratulations to Ladbaby. It is a superb achievement to score an official Christmas number one once, let alone twice in successive years.
"And to do so with increased sales year on year is quite phenomenal - and all for a fantastic cause.
"Of course, commiserations to Stormzy, Lewis Capaldi, Dua Lipa and Wham! who made up the official top five in what has proven to be a genuinely competitive race, which has ended up spanning generations and genres."
Stormzy's single Own It with Ed Sheeran and Burna Boy is at number two, Capaldi's Before You Go is at number three, Lipa's Don't Start Now is at number four and festive classic Last Christmas by Wham! is at number five.
Over on the album chart, Sir Rod Stewart has scored this year's Christmas number one album.
The veteran music star's latest record You're In My Heart with the Royal Philharmonic Orchestra has scored a second week in the chart top spot, fending off competition from Stormzy's hotly-anticipated second album Heavy Is The Head and One Direction star Harry Styles' second solo album Fine Line.
Sir Rod said in a statement: "Two weeks in a row at number one, plus this week as the number one Christmas album makes me happier than a dog with two dicks."
It is his 10th number one album, and he is now only the fifth British act in UK chart history to have as many chart-topping records.
The Beatles, Robbie Williams, The Rolling Stones and David Bowie are the only other British acts with more number one albums.
Stormzy has entered the charts at number two with his album, with Styles in third place.