Ravenhill arrived at Northampton's Sixfields Stadium this Wednesday to complete the move after being permission by City boss Phil Parkinson to talk to the Cobblers.
Parkinson has also given Northampton permission to play Ravenhill in this season's F.A Cup with Budweiser, meaning the midfielder could make his Cobblers debut in their first round tie at Bishop's Stortford this Sunday.
Ravenhill's temporary move to Northampton comes after the experienced midfielder was told by Parkinson last month that he would be allowed to leave the Coral Windows Stadium if the opportunity for first team football came up elsewhere.
The former Doncaster Rovers, Darlington and Notts County campaigner has only started two games for City this season - the Capital One Cup tie at Huddersfield Town back in August and the Johnstone's Paint Trophy match against Hartlepool United in early September.
Picture kindly provided by Northampton Town
The move to the Sixfields Stadium will see Ravenhill reunited with former City team-mate Matt Duke, who joined Northampton from the Bantams this summer.
After losing to City in the League 2 Play-Off Final last season, Northampton find themselves bottom of the table following a run of only two wins from their opening fifteen league games.