Tony-winning star Jessie Mueller will depart the show this March.
Other parts in the musical will also be cast for the Broadway, touring, and international productions.
The hit Broadway musical opens in London in February 2015.
Mueller's Tony-nominated costars Jarrod Spector and Anika Larsen have also extended their contracts.
Campbell will replace Jake Epstein in the role of Gerry Goffin.
The new musical will open in the West End at London's Aldwych Theatre in 2015.
Larsen plays Weil on Broadway in Beautiful — The Carole King Musical. Both have written work for the stage, but only one of them considers herself a "writer."
Jerry Seinfeld, Bernadette Peters, and Clive Davis were also on hand to cheer for Jessie Mueller and the cast of the new musical.