The 46-year-old was appointed back in June following an excellent season with Barnsley, leading the Tykes to the play-offs.
Although they lost in the semi-finals, it was enough for Ismael to be offered the Baggies job, who had been relegated from the Premier League, starting well at the Hawthorns, defeating the Hatters 3-2 in his first home game and going unbeaten in the league for the first two months, with six wins and four draws.
Albion then lost 1-0 at Stoke, starting a run of four defeats from eight, before securing back-to-back victories over Coventry and Reading in December.
Since then though, the Baggies have only won won out seven matches, taking five points from a possible 21 to sit in fifth place, trailing the automatic promotion places by eight points.
They also sit just three points above Luton, whom they visit later this month, with Town having a game in hand over their rivals.
A statement on the club's official website said: "West Bromwich Albion Football Club can confirm Valérien Ismaël has today left his position as head coach.
"Assistant head coach Adam Murray has also departed The Hawthorns.
"The club would like to place on record its thanks to Valérien and Adam for their efforts and wishes them well in the future.
"The process of recruiting a new head coach is now under way and an appointment will be announced in due course."