27-year-old midfielder Danny Rose has been signed on a deal until the end of the season after being released by Chris Wilder's former club Oxford United.
The Northampton manager has also extended Lee Martin's loan stay at Sixfields from Millwall, the winger having impressed in his short time with the club to date.
Defender Evan Horwood has been allowed to join promotion-chasing National League side Grimsby Town on loan for the remainder of the campaign.