The Hollywood star, 50, is being flown in especially even though the movie's soundtrack is not nominated.
A music insider said: “Brits bosses did everything they could to sign up Hugh.
“He may not be as cool as the younger stars performing on the night, but he will certainly be the most popular.
“They are banking on his opening performance being a must-see for fans of the movie and are convinced he will be enough to persuade older viewers to tune in.
“Because it was a soundtrack it didn’t fit into any obvious awards categories but it has been the biggest thing in music for years so they had to acknowledge it somehow.”
He played circus ringmaster P.T. Barnum in the hit 2017 film, which also starred Zac Efron and Michelle Williams.
The soundtrack to The Greatest Showman, which features songs This Is Me and Never Enough, was the biggest selling album of 2018 in the UK with 1.6million sales.
It sold 900,000 more than Staying At Tamara’s by George Ezra, who will also perform at the ceremony, which was No2 in the annual totals with sales of 691,000.
Little Mix, Calvin Harris, Dua Lipa and Pink will also perform at the ceremony in London’s O2 Arena next Wednesday, hosted by Jack Whitehall live on ITV.