"I have been fortunate to be able to call on the experience of Malcolm Crosby and so far things have gone well for us," said Sampson.
"We are battling hard to try to catch the top seven and get ourselves into the play-offs this season.
"I have been delighted with the reaction of the players and the supporters since taking over. I am pleased we have got this sorted out."
Northampton chairman David Cardoza said he was pleased to give Sampson an extension to his contract, which had been due to expire at the end of the season.
Ian is Northampton Town through and through and his commitment to the club has never been in doubt
Northampton chairman David Cardoza
"Ian has been a breath of fresh air," Cardoza said.
"Many people know Ian is Northampton Town through and through, and his commitment to the club has never been in doubt.
"Since he has taken over as manager, he has impressed me greatly.
"Our performances have improved, our results have improved, he has shown great faith in the young players here and we have seen any number of players improve and progress under his leadership.
"The team spirit is great and it is clear the players are responding to him and the professional atmosphere he has generated and instilled."
Cardoza was also quick to recognise the club's debt to Crosby, who was an assistant to Gareth Southgate and reserve team manager under Steve McClaren at the Riverside.
"[Ian Sampson] is being ably assisted by Malcolm Crosby, and his experience is proving invaluable to us.
"His work both behind the scenes and on the training field should not be underestimated and the two of them make a very good partnership."
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