Starting Friday, he will be seen playing Ridge Forrester, a character Ronn Moss originated in 1987 and played until last year.
Kaye is a daytime television veteran known for his work on "One Life to Live," "Port Charles" and "All My Children."
"Thorsten's powerful screen presence and vast range as an actor has intrigued me for years," "The Bold and the Beautiful" executive producer and head writer Bradley Bell said in a statement Monday. "The timing was right, so I took the opportunity to cast him in the role of Ridge Forrester. I'm confident Thorsten will make this role unique on every level."