The 46-year-old former Mainz player took charge at Signal Iduna Park in 2008, leading them to two Bundesliga titles, a DFB-Pokal Cup and the UEFA Champions League final last season.
Klopp is under contract at the club until the end of 2016, but Watzke says he has a job for life if he wants to stay in Dortmund.
"I would never sack Jurgen Klopp," Watzke told Kicker Sportmagazine. "Never, no way! I know he does not sign contracts to break those deals.
"Klopp has never done that at any time. He is under contract with Borussia Dortmund until June 2016.
"He will always honour the deal. There is no doubt about that."