The facility in Morden says it has received the official designation from the Guinness World Records organization.
Mosasaurs were the largest and most ferocious marine predators during the late Cretaceous period 80 million years ago.
With four sets of enormous teeth, some scientists refer to mosasaurs as the "Sea-Rex" because of its status as top predator.
The fossil on display in Morden is affectionately named "Bruce" and is just over 13 metres in length.
Peter Cantelon, executive director of the fossil centre, hopes the designation will draw more visitors to the facility.
"Once our research confirmed the size we immediately started thinking about pursuing a world record," Cantelon said Wednesday.
"It is great for people to be able to come and see something here in Morden that cannot be seen anywhere else on the planet."
The centre says it has the largest collection of marine reptile fossils in Canada.