The 19-year-old recently returned from a five-month absence following a broken ankle, which he suffered in the first match of the Scottish Premiership season.
And his new contract comes as a welcome boost on top of his return to fitness, having made just two substitute appearances under Terry Butcher.
The teenager, who has made 19 first-team appearances, said: "From day one, I wanted to stay at the club. I have progressed here for 10 years now. I wanted to sign to keep moving forward with Hibs.
"The first thing I wanted to do was get back to fitness, but getting my contract signed and getting my future resolved was an added bonus.
"Talks started with Pat Fenlon and when the new manager came in I wasn't sure what was going to happen, but he sat down with me and told me he was looking to sign me. It was great to hear that I'm wanted at the club."
Despite a shortage of match-fitness, Harris was thrown on in the ninth minute of Hibernian's 3-2 defeat by St Mirren on Saturday when Ryan McGivern went off injured.
And he is looking to push on when Celtic visit Easter Road on Sunday.
Harris said: "It was my first real injury, so it was a bit hard to take at the start and I was a bit unsure what to do. I had a lot of time in the cast and a lot of fitness work but I'm just relieved to be back playing football.
"It was a surprise to get on on Saturday when Ryan got injured, but the manager showed faith in me and it was great to be back in front of the fans.
"It was a disappointing first half hour but it was great to be back at Easter Road.
"I'm still a young boy and I still have a lot of time to develop. The injury was disappointing but I'm raring to go now and I just want to kick-start my season."
McGivern and fellow defender Paul Hanlon are both out injured for the visit of the champions along with centre-back James McPake, but Butcher is hopeful of adding a new face to his squad before then.
Butcher said: "There is now news yet, we are still working very hard and we are optimistic that we can get something done before the weekend."
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- Terry Butcher