Caulker's £8million switch is expected to be completed in due course, as the former Swansea man looks set to pair up with Rio Ferdinand in the R's defence for the coming season.
QPR manager Harry Redknapp had gone public in his admiration of Caulker, who has one England cap to his name, as well as stating a belief that playing alongside Ferdinand would strengthen the 22-year-old's England credentials.
Since relegation for Cardiff was confirmed back in May, it has long been thought that Caulker would not be on their books by the start of the 2014/15 season.
Caulker has also been linked with moves to Crystal Palace and Southampton, although the strength of the interest of the two sides remains undefined.
On Monday morning, Caulker commenced medical testing before putting pen-to-paper on what is expected to be a four-year deal with the West London club.
If the deal goes through as us expected, Caulker will become QPR's second summer signing, after the club completed the signing of 35-year-old free agent Ferdinand following his release from Manchester United at the end of last season.