Steve Bruce became the first Premier League manager to be sacked this season when Sunderland announced they had parted company with the former Manchester United player on Wednesday.
Bruce, 50, joined Sunderland from Wigan Athletic in 2009 and leaves with the north-east club languishing two points above the drop zone.
"Sadly results this season have simply not been good enough and I feel the time is right to make a change," chairman Ellis Short said on the club's website.
"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 that I have taken lightly."
Bruce guided Sunderland to 13th in his first season in charge and improved on that with a 10th-placed finish in 2010-11.
American businessman Short, who took over the club in May 2009 and became the chairman last month, paid tribute to Bruce's hard work.
"Steve has acted with honesty and integrity throughout, which is testament to the character and commitment he has shown during his time at Sunderland," he said
"I would like to personally place on record my thanks to him for his significant contribution to our football club...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."
Short added that assistant manager Eric Black would take charge of the first team duties as the club searches for a new manager.
Former Aston Villa boss Martin O'Neill and ex-Fulham manager Mark Hughes are the early favourites with bookmakers.
Bruce, whose last match in charge was a 2-1 home defeat by ex-club Wigan, was hampered by striker Asamoah Gyan making a loan move to Al Ain in the United Arab Emirates in September when the transfer window was already shut.