Jardim had achieved immediate success with the club, guiding them 10 points clear at the top of the league.
However, the club have seen fit to dispense with his services ahead of the game against PAS Giannina tomorrow.
"Olympiacos FC have parted company with Leonardo Jardim and the manager's contract has been terminated with immediate effect," read a club statement. "We wish to thank Mr Jardim for his work and efforts during his time at the club.
"Assistant coach Antonis Nikopolidis will step in to take charge of the team for tomorrow's match against PAS Giannina."
Jardim left his previous club FC Braga in May last year.