"He's a ball-playing midfielder who can create things," said Cobblers manager Ian Sampson. "We are willing to give him a chance and an opportunity,
"We are always looking for players that we feel will improve the squad and I feel Kevin will do that.
"He is a good footballer and I am sure he will fit in well."
Thornton left Coventry by mutual consent in July, shortly after being convicted of a drink-driving offence for being over twice the legal limit.
Thornton also pleaded guilty to having no insurance, failing to stop at the scene of an accident and not having a full driving licence.
The Irish midfielder was handed a 22-month ban from driving, fined £2,750 and ordered to pay £260 in costs.
After leaving the Sky Blues, Drogheda-born Thornton, who also spent three months on loan at Brighton while at the Ricoh, then re-signed for his former club Boyne Rovers FC in Ireland.
Thornton becomes Sampson's third January signing after capturing another Irishman, striker Stephen O'Flynn from Limerick, and defender Luke Wilkinson on loan from Portsmouth.
Source: BBC Sport
Source: BBC Sport