The Cobblers expect to sign their former skipper on a permanent deal before the weekend.
Carlisle, whose second loan spell at Sixfields concluded with the win over Aldershot on December 22, is a free agent after his six-month contract at npower League Two rivals York expired.
The centre-half, 33, is expected to go straight back into the matchday squad on Saturday after missing the New Year's Day win over Dagenham because he could not be registered as the transfer window was closed.
Manchester City loanee Emyr Huws' deal expires after the game against the Cod Army while Northampton's other three other loan players - Danny East (Hull), Henoc Mukendi (Liverpool) and Chris Smith (Swindon) - have all now returned to their parent clubs.
Injured defenders John Johnson (knee) and David Artell (Achilles) are scheduled to resume full training on Monday.