The 20-year-old, a product of QPR's youth academy, trained at the Perth club last week and impressed manager Steve Lomas.
He has now joined the Saints on loan and could be involved against Aberdeen on Wednesday night, depending on international clearance.
Doughty told the club's official website: "I'm really looking forward to this. I enjoyed my spell up here last week - the training was good and the boys made me feel welcome."
The midfielder has made just one senior appearance for QPR in the FA Cup defeat to Blackburn back in 2011 and has taken in loan spells at Woking, Crawley and Aldershot.
Manager Lomas said: "It is good to get another body in for the rest of the campaign.
"We had Michael up here in Perth for a few days last week to have a look at him and give the lad a chance to see what we are all about.
"He is keen to make an impression and can play anywhere across the middle.
"QPR want him to get more experience and this is a move which could benefit all parties."