The 22-year-old will link up with Alan Archibald's side until the end of the season, with Thistle currently sat 11th in the SPL.
Cargill makes the move following his return from Fleetwood, where he made 18 appearances and netted one goal during a six-month spell.
Meanwhile, Bournemouth boss Eddie Howe is yet to make a new loan decision for goalkeeper Ryan Alsop.
The 25-year-old spent the first half of the season at League One Blackpool, where he made 23 appearances. He returned to Vitality Stadium earlier this month.
Howe told the Daily Echo: “I wouldn't rule it out at this stage but let's wait and see.
“He had a good, productive spell with a lot of games at Blackpool, which we were pleased with and we will see what happens next."