Former Tottenham defender and Northampton manager Colin Calderwood described the 20-year-old as "a dogged individual who will fight and stand his corner" after making his debut at the weekend.
Although Barnard, scorer of 11 goals in 14 appearances for Tottenham's reserves this season, didn't get on the scoresheet on Saturday, the Cobblers beat Macclesfield 1-0 at home.
"Because of the bad weather, he could not get here until after training on Friday but he did very well.
"We had an untried pairing with Lee and Danny Crow but they were excellent, especially in the first half," said Calderwood.