The Mumbo Jumbo ride at Flamingo Land plunges down an incline of 112 degrees from a high point of 30m (98ft).
A Guinness World Records adjudicator is set to ratify the record on Saturday when the ride opens to the public.
Park chief executive Gordon Gibb said: "You'd have to travel to Indiana Beach in the US to come anywhere close - even then, ours is steeper by one degree."
Passengers on the new rollercoaster, which cost £5m to design and build, will pull about 4Gs, close to levels experienced by jet pilots.
Explaining the Mumbo Jumbo name, Mr Gibb said: "It's meant to be a tongue-in-cheek description of the way other theme parks boast about their new rides.
"We're not talking mumbo jumbo, our new rollercoaster is the real deal."
Guinness World Records said the ride would be added to its "steepest rollercoaster made from steel" category after ratification on Saturday. | 