Chairman Tony Bloom said the Premier League club and De Zerbi "have mutually agreed" that the Italian will depart.
"Roberto has given us two excellent seasons of service in which he has led the club to new heights, not least our first ever European campaign which will live long in the memory of Albion fans," said Bloom.
"We have mutually agreed to end Roberto's contract at a time that suits both parties allowing us the earliest opportunity to plan for next season, and Roberto plenty of time to consider his next move and his future."
Bloom added: "I am sure our fans will give Roberto and his staff a wonderful and fully deserved send off at the Amex before, during and after tomorrow's match.
"In the meantime, I'd like to thank Roberto and his staff for all their hard work in the past two seasons. They all leave our club on good terms and with our very best wishes for the future."