The 29-year-old right-back, who is out of contract at the end of next month, did not start a league game during the 2021/22 season, making five substitute appearances in addition to three cup outings.
However, he remains a popular figure with supporters and was often praised for his attitude and professionalism by manager Jon Brady. Harriman joined the Cobblers as a free agent in September 2019 and played 75 times across the following three seasons.
He will be best remembered for producing two brilliant performances in the play-offs in 2020. He played a key role in helping the Cobblers overturn a 2-0 first-leg deficit to beat Cheltenham 3-2 in the semi-finals before starring at Wembley in the final.
Confirming his departure on Twitter, Harriman said: “What can I say after three years it’s time to leave the @ntfc family. It’s been an absolute pleasure to share some fantastic and unforgettable moments with you all. I hope that I done my best every time I put on that shirt. I wish you all the very best next season. Thank you.”
The full retained list is expected to be confirmed later on Friday.