The Belgian midfielder has become a key player for the Edinburgh club since arriving in September last year, with head coach Robbie Neilson labelling him “immense”.
Djoum’s existing deal was due to expire in ten months time, but he has now committed another two years of his future to Hearts.
“Arnaud has been immense for us since joining last season,” Neilson told the Hearts website. “His quality is there for all to see and I’m really pleased to tie him down until 2019.
“We were lucky to get him in the first place, to be honest. He’s a real talent with great technique and vision. He’s also proved himself to be a proper team player, with an eye for goal thrown into the mix.
“I’m convinced the best is yet to come from him and can’t wait to see him in action this season.”