The centre-back becomes Northampton's second January signing after Chanka Zimba and will spend the rest of the season on loan at Sixfields.
The 23-year-old has made seven first-team appearances at Ewood Park, four of which have come in the Championship this season, after emerging through Blackburn's youth ranks and captaining the U23s team.
He played five times on loan at Rochdale in 2019/20 and then made 10 appearances during another temporary stint with Hartlepool United last season.
Magloire also spent time north of the border with Motherwell when playing 12 times for the SPL club in 2020/21.
Pace is overwhelming Magloire's standout attribute. Back in 2019, he clocked a top speed of 10.6 metres per second, faster than PSG star Kylian Mbappe.
"Nobody beats him in a foot race," said Blackburn boss Tony Mowbray.