Press Association Sport understands Rangers paid a loan fee of ?200,000 to secure the services of the 25-year-old winger. Reports emerged on Thursday that the last-gasp deal for Puncheon had not been completed before Wednesday night's transfer deadline but the move has now been confirmed by both parties.
"It just made sense to give him an opportunity to come in until January and show us what he can do," manager Neil Warnock told the club's official website, www.qpr.co.uk.
"This all happened very late in the day so I am very pleased we got him in. Jason is a good acquisition because he brings pace and plenty of desire.
"To be perfectly honest, he was so keen to come to QPR I think he would have paid us!
"He is desperate to do well, and that really impressed me."
Puncheon spent loan spells with Millwall and Blackpool last season after finding himself pushed to the fringes at St Mary's by 17-year-old starlet Alex Oxlade-Chamberlain.
The winger returned to Saints this summer but did not go on the club's pre-season tour to Switzerland and has not been given a squad number.
The Croydon-born player attracted the attention of QPR during the summer and a deal was completed just before the 11pm deadline after a late move from the recently-promoted side.
Puncheon's move is pending Premier League approval but once complete could see the former MK Dons man make his debut against Newcastle.
Source: PA
Source: PA