O'Donovan, who worked under Cobblers boss Aidy Boothroyd at Coventry, has joined the npower League Two promotion chasers until the end of the season.
The 27-year-old is one of a handful of options for Boothroyd should he wish to make changes to his starting XI following the midweek defeat to Gillingham.
Fifteen-goal striker Adebayo Akinfenwa is pushing for a recall while full-back John Johnson was also among the substitutes at Priestfield after several weeks out with a knee injury.
The versatile Emmanuel Oyeleke could also make his debut after failing to get off the bench on Tuesday night following his loan arrival from Brentford.
The trip to the New York Stadium is the first of six npower League Two fixtures facing the Cobblers in February and Boothroyd said: "It is going to be a big month.
"What we've done up to now is good and we would have certainly taken it at the start of the season but it's only the start of February and we've still got 17 games to go."