The back row forward, who turned 29 last Sunday, started out as a raw Academy flanker having been scouted by Dylan Hartley during the 2011 Rugby World Cup in New Zealand.
But as time went on, Saints’ need at No.8 grew, with the likes of Samu Manoa and Louis Picamoles departing to leave a sizeable void.
Harrison, as he has made a habit of doing since making his debut against Wasps in March 2012, stepped up in style.
He hit the headlines for his showings at No.8 during the 2015/16 campaign, which was certainly a stellar one for the Opotiki-born ace.
Harrison won awards galore, sweeping up at the end-of-season dinner as he scooped the breakthrough player, supporters’ player and players’ player prizes.
He was named in the Premiership dream team that season and he has continued to be a staple part of the Saints first team ever since, predominantly donning the No.8 shirt.
But with big South African No.8 Juarno Augustus drafted in this summer, Harrison may be utilised slightly more at six or seven, taking him back to his Northampton roots.
And that is not something that fazes him at all.
“Juarno is a good boy and most importantly he’s a really good rugby player,” Harrison said.
“It’s good competition for me and it pushes me to learn six and seven again.
“I’m hoping we can get a good partnership and it felt really good playing alongside him at Bedford last Friday night.
“I’ll obviously be fighting for my spot and I’ll also be fighting for a spot to play alongside him.”
Harrison loves a scrap. He fights for every single blade of grass on a weekly basis at Saints.
And his development from dreadlocked youngster to key first-team player has been hugely impressive.
“I’ve had 10 years here and I’ve loved every minute,” Harrison said.
“I hope I can stick around for a lot longer.
“It’s awesome, what more can you ask for from a club? We’ve got a good group of boys around us, good coaching staff and good fans.
“Everything around here is wicked and that’s why so many people want to stick around.”
Harrison was in action at Bedford last Friday, bringing back memories of his younger years.
He was part of the Saints squad that travelled to Goldington Road for a pre-season fixture against the Blues back in 2013 - and they would go on to win the Premiership title at the end of that campaign.
“I remember bits of that game,” Harrison said.
“I remember it was the first time I played against Paul Tupai. Him and Dylan (Hartley) looked after me the first time I came over so it was pretty cool.
“I expected it to be a bit of a friendly but then he came in and absolutely belted me so it was a nice warm welcome really!
“I do remember snippets of that game and one of the bits I remember was the tackle from Courtney (Lawes) on that 10.
“It was nice to be back there last Friday. It’s an awesome ground and the support’s amazing.
“We had more than 3,000 fans there last week and it looked like it was full all the way around so it was nice to be back.
“It was funny because when I got yellow carded near the end I could hear a bit of abuse when I was coming off and I was thinking it’s nice to have fans back.
“I was absolutely hanging at the end there but it was nice to be back out there, especially with crowds.
“I was out of the last two games we had last season so I didn’t get to play in front of them then.”
Harrison is now looking forward to running out in front of the Franklin’s Gardens faithful when Ospreys come calling for the second and final pre-season match on Friday night.
And he is desperately hoping that he can put the frustrations of an injury-plagued 2020/21 season behind him.
“Personally, it was very frustrating,” said Harrison, who was only able to make 11 appearances for Saints during the previous campaign.
“There were actually some stats that came out and over my career I’ve missed 500 days of rugby, which is relatively low. But last year I missed 140 of those so it sort of summed it up.
“I was plagued with injuries. I would come back, get good form, get a good run and then I would get injured again so it was frustrating for me.
“I’ve had to change up the way I do things. I’ve got more into my rehab, more into my nutrition but it’s been a nice shake-up and I feel good and I feel energised.
“It’s definitely something I’ve had to focus on but I think I’m reaping the rewards now.
“Hopefully I can stay fit for this season.”
Having sampled that Premiership glory in 2014, Harrison has been desperate for more ever since.
But Saints have often been blighted by inconsistency and they eventually finished fifth last season, 14 points adrift of fourth-placed Harlequins, who went on to win the title.
“We had some stats and if you come third or fourth the chances of you winning away in a semi-final is slim, unless you’re Harlequins,” Harrison said.
“We always want to push for top spot but first or second, that goal doesn’t really drift.
“The last couple of seasons we’ve always said we’re a young team coming through but we’re not that young team any more.
“We’ve got to start pushing on and we’ve got to start getting to where we should be.”