The Spaniard replaced Arsene Wenger in May 2018 but failed to turn around the club’s fortunes during his 18-month spell in charge.
Its 2-1 defeat to Frankfurt in the Europa League Thursday was the side’s seventh consecutive game without a win and Arsenal has slipped to eighth in the English Premier League.
In truth, pressure had been mounting on the 48-year-old for weeks with large pockets of fans questioning his tactical direction and calling for him to be sacked.
The club said the decision was made “due to results and performances not being at the level required.”
“Our most sincere thanks go to Unai and his colleagues who were unrelenting in their efforts to get the club back to competing at the level we all expect and demand,” said Arsenal director Josh Kroenke.
“We wish Unai and his team nothing but future success.”
Former player and current first-team coach Freddie Ljungberg will take over on a temporary basis as the search for the new head coach gets underway.
“We have a busy few weeks ahead and the team needs your support. Let’s get to work!”
Arsenal’s next game is away to Norwich City in the EPL on Sunday.
Emery, who has previously managed the likes of Paris Saint-Germain and Sevilla, was brought to the Emirates to win trophies and reinsert the club as a dominant force in Europe.
The initial signs were positive as Arsenal reached the final of the Europa League in his first season in charge — a competition the manager has won on three occasions — but defeat to Chelsea meant yet another season out of the prestigious Champions League.
However, the new star has barely made an impact in his first season at the club and Arsenal’s defensive frailties have continued to hamper the team’s ambitions.
Despite Emery being booed by fans during his final weeks in charge, anger has also been directed at the club’s hierarchy, with supporters pointing towards a lack of ambition on the pitch.
The thousands of empty seats for Emery’s last game in charge demonstrated the negativity now rife throughout the club’s fan base. Against Frankfurt, the official attendance was more than 49,000 but several reports said the real number was around 25,000.
Arsenal Supporters’ Trust said the dismissal “inevitable” but called for change in the club’s structure.
“This means that the club needs to be governed by a strong Board in London, one that is truly independent and has the expertise and dynamism to drive a football club forward.”
It added: “So if Arsenal are to genuinely move forward from today it requires not only a new head coach appointment but also a rejuvenation of the boardroom.”