Baptiste, 31, has put pen to paper on a two-year deal and teams back up with manager Ian Holloway, who he worked under during his time at Blackpool.
“I know him really well and know what he can bring to our squad, so I’m delighted he’s signed and I’m looking forward to working with him again,” Holloway told QPR’s official website.
“He’s versatile, he can play anywhere across the back and that was a big plus for me.
“And the fact I know him – and he knows me – and I know I can rely on him too, means he’ll be a big addition to the group.”
Baptiste, who could make his QPR debut in Tuesday’s home Carabao Cup tie against Northampton, progressed through Mansfield’s youth system and made over 160 appearances for both them and Blackpool.
He has also had spells at Bolton and Blackburn and spent last season on loan at Preston, for whom he made 24 appearances.