The 29-year-old joins for a reported fee of £1.25million, which triggered a release clause in his Seasiders contract.
Campbell, who spent his early playing days in west London, becomes manager Neil Warnock's fourth summer signing.
The striker told his new club's official website, www.qpr.co.uk: "It's a club that I supported as a kid. I grew up around here and QPR have played a massive part in my life.
"This was my first club, from six to 16, so to finally be back here at the age of 29 is really special."
He added: "It's a massive club and it means a lot to me to be back here where it all began.
"There were other clubs in the Premier League that showed an interest but when I heard QPR were in for me it was an offer I couldn't refuse - this is my club."
Rs boss Neil Warnock added of his new number nine: "He is someone I have admired for a while now and he had a fabulous season in the Premier League with Blackpool last year.
"He is a QPR fan and you can tell he has a great desire to do well for the club he supports. That shone through when I met up with him - he can't wait to play for us.
"He also gives us that extra element of pace which we need and I am sure he will prove to be a big hit with the fans at Loftus Road this season."
Source: PA
Source: PA