The 20-year-old Nigerian, who was without a club after a spell at Dulwich Hamlet, scored 11 goals in 18 games for the Cottagers Under-18 team in 2008/09.
"Michael is quick, tenacious and a real pain for defenders to play against," Cobblers manager Gary Johnson told the club's website.
"He has been training with us this week and has impressed."
Uwezu, who started his career at Arsenal but signed his first professional contract with Fulham, spent a loan spell at Lincoln City last season.
"Michael first came to my attention when he was in the reserves at Fulham," continued Johnson. "I was aware of him when I was at Peterborough.
"He was offered a contract to go and play in Holland, but he turned that down to come and join us for the rest of this season to try and earn a contract for next season.
"He has got a terrific work ethic."
The striker will not be available for Northampton Town's match against Torquay United on Saturday, because the deadline for registration for that match passed at noon on Thursday, but he will be available for the trip to Accrington Stanley on Saturday, 2 April.
Source: BBC Sport
Source: BBC Sport