Warnock, who was appointed in March 2010 and won 33 of his 84 matches in charge, guided the West London club back to the Premier League for the first time in 15 years last season.
Malaysian owner Tony Fernandes said in a club statement: "Sadly a recent run of poor form has seen us slip alarmingly down the table and the board felt it was the right time to make a change.
"Neil Warnock has acted with honesty, professionalism and integrity throughout his time at the club and I would personally like to thank him for his significant contribution to Queens Park Rangers over the last 22 months.
"I genuinely wish him all the very best for the future and he will always be welcome back at Loftus Road."
Vice-chairman Amit Bhatia said the announcement was made "with a heavy heart" while Fernandes told his 147,000 Twitter followers that it was "a sad day for me too."
"Trust me in my 47 years of life I have never had to make such a tough decision," he added.
Chief executive Philip Beard told Sky Sports television that staying in the Premier League was key to the club's ambitions and they would move swiftly to appoint a new manager.
"I understand the fans are going to have a mixed reaction to this," he said of Warnock's departure. "Our intention will be to bring somebody in who can grow the club and fulfill ambitions."
Warnock's sacking was announced shortly after the draw was made.
Warnock said in a statement "Obviously I am very disappointed but having achieved so much I leave the club with a great sense of pride."
