Chairman Ellis Short acts with the club just two points above Premier League relegation zone after defeat at home to Wigan Athletic.
Sunderland part ways with manager Steve Bruce
Sunderland have parted company with manager Steve Bruce after chairman Ellis Short described results this season as "simply not good enough."
Saturday's home defeat to Wigan Athletic left Sunderland 16th in the English Premier League, just two points above the relegation zone.
Bruce had insisted he had no intention of walking away from the Stadium of Light, despite fans calling for his head at the weekend.
In a statement released on the club's official website, Short said: "This has been a difficult time for everyone at Sunderland and is not a situation that any of us envisaged or expected to be in.
"It is my job as chairman to act in the best interests of our football club at all times and I can assure everyone that this is not a decision I have taken lightly.
"Sadly results this season have simply not been good enough and I feel the time is right to make a change.
"Steve has acted with honesty and integrity throughout, which is testament to the character and commitment he has shown during his time at Sunderland.
"I would like to personally place on record my thanks to him for his significant contribution to our football club over the past two and a half years and everyone here at Sunderland naturally wishes him the very best for the future.
"I would also like to thank our fans, who have endured a trying start to the season. Their support continues to be the driving force behind our club and is vital as we now look to the future."
Eric Black, the assistant manager, will take charge of the team while the search for a new manager begins.
Sunderland travel to Wolverhampton Wanderers on Sunday, one of a series of four games which Bruce had targeted to help his side climb the table.
However, a dire 0-0 draw with Fulham was followed by Saturday's defeat to then-bottom Wigan, who snatched a last-minute winner following a blunder from Wes Brown.
Following the weekend trip to Molineux, Sunderland are at home to fellow strugglers Blackburn Rovers.
Former Aston Villa manager Martin O'Neill - a boyhood Sunderland fan - is an early contender to replace Bruce, along with the likes of Mark Hughes and Rafael Benitez.