Sunderland are 17th in the 20-team league with 26 points, one place and one point above the relegation zone with only nine matches left to play.
They have won only one of their last 12 league games.
“I would like to thank Gus for his endeavours during his time at the club, in particular last season’s ‘great escape’ and cup final appearance, which will live long in the memory of every Sunderland fan,” chairman Ellis Short said in a statement on the club website (南宁夜网.safc广西桑拿,).
“Sadly, we have not made the progress that any of us had hoped for this season and we find ourselves battling, once again, at the wrong end of the table.
“We have therefore made the difficult decision that a change is needed.”
The 46-year-old Poyet, who had been in charge at the Stadium of Light for 75 matches since October 2013, saved the Black Cats from relegation last season when they won four of their last five games to escape from the bottom three and finish 14th.
He also steered them into their first major final for 22 years although they were beaten 3-1 by Manchester City in the League Cup at Wembley.
But the Uruguayan has become the sixth Premier League manager to leave this season with Sunderland winning only four of their 29 league matches.
Defeats included an 8-0 loss at Southampton, the joint worst in their league history, while Saturday’s reverse to Villa was their heaviest at home since 2007.
Poyet succeeded Paolo di Canio as manager with the team bottom of the Premier League and although their results improved slightly after his arrival they were still bottom of the table with five matches to play.
Unlikely wins at Chelsea and Manchester United, however, as well as home victories over Cardiff City and West Bromwich Albion secured their top-flight place for an eighth successive season.
Poyet antagonised Sunderland’s fans this season by saying they were “living in the past” and thousands streamed out of the ground as they went 4-0 down to Villa before halftime. Some angry supporters had to be restrained as they headed towards Poyet in the dugout.
(This version of the story corrects Poyet’s age to 46 in sixth paragraph)
(Editing by Ed Osmond)