The 28-year-old defender has left for Loftus Road with Town poised to sign a replacement in 1860 Munich captain Christopher Schindler.
With only a year left on his deal under head coach David Wagner, Town have cashed in on the interest in the Wales international, especially as he was keen to move on and return south.
“Since the end of last season, Joel’s representatives have been pushing hard for this transfer to happen,” said Town head coach David Wagner.
“As I have said throughout the summer window, we were under no pressure to sell any player, but we had to consider that Joel’s contract was finishing in June 2017.
“We are happy that the transfer is great value for a defender who has one year remaining on his contract.”
Wagner, whose squad have just returned from a ‘bonding’ trip to Sweden, added: “I must also say thank you to Queens Park Rangers.
“We told them that we wanted this transfer completed quickly and they have been very respectful to that wish.
“I would like to say good luck to Joel, too, as he leaves to join Queens Park Rangers.
“He has been at the club over four years and was an important part of my team over the past seven months.”
With Schindler’s move on the horizon, Wagner added: “We have been planning for the possibility of Joel leaving for a long time and we will make another addition shortly to add a fourth centre-back alongside Mark Hudson, Michael Hefele and Martin Cranie.”
Lynch has done a lot of work with the Town Foundation and chairman Dean Hoyle thanked him for his contribution on and off the field.
“He’s been a regular figure in the team over the last four years, off the pitch and just as importantly off it,” said Hoyle.
“He has given up countless hours working for our charity, the Town Foundation. All the best to Joel at QPR.”
Born in Eastbourne, Lynch began his career at Brighton, making 79 appearances before a 2009 move to Nottingham Forest, where current QPR boss Jimmy Floyd Hasselbaink was on the coaching staff.
He played 80 times for Forest, initially on loan, before joining Town under Simon Grayson following their return to the second-tier after victory over Sheffield United in the play-off final at Wembley.
Lynch, who made 40 appearances for Town last season and was popular with fans, totalled 129 appearances in the blue and white stripes, but he could have walked out for free at the end of the coming campaign.
At QPR, Lynch could be lining up alongside former Town teammates Alex Smithies and Jack Robinson.