The flanker, who turned 20 at the start of September, arrived in Northampton last November after completing his studies at Rotorua Boys School. Although born in Opotiki, on New Zealand's north coast, Harrison qualifies for England through his Nottingham-born father and he believes that his future is very much in the East Midlands.
"I've still got to get used to this weather but all in all I'm loving my time here," he said. "I'm very excited by my new contract and it offers a lot of opportunities for me. Hopefully I can get some games during the season.
"I've thoroughly enjoyed my time in Northampton so far, and obviously my main aim is to try and get into the first team here at the Saints. That's what I'm focusing on at the moment."
Director of rugby Jim Mallinder said that Harrison, who already has four first team appearances and one Aviva Premiership Rugby try to his name, had impressed in his short time at the club.
"Teimana has the hunger, desire and quality to be able to succeed in the Premiership," he said. "When he arrived we could see straight away that he had all of the skills and raw talent, and now that he has had a full pre-season under his belt he is starting to take that to the next level.
"We have had no hesitation in offering Teimana a full contract for the next two years, and hopefully he will remain a part of the Saints squad for a long time after that."