He will join up with the GUINNESS PRO12 side on his return from this summer's tournament in Italy.
Kinghorn said: "I spent time with Edinburgh before I went to the FIRA championship [with Scotland under-18] and that was a really good experience, seeing the day-to-day life of a club. Everyone was really welcoming and friendly and it's a great environment to be going into.
"It's been really good to see the club do so well over the back end of the season, with their form in the GUINNESS PRO12 and the Challenge Cup final at the weekend."
The Edinburgh Academy pupil, and current captain of the school's 1st XV, started playing aged ten, after an earlier fascination with the round ball.
He said: "When I was younger football was my main interest, then I started to play rugby at school. Some of my mates went to play for Currie so I went along with them, then things escalated at under-16 level, I began playing for the school first XV and since then it's been my goal to play professionally.
"I've been doing kicking practice at BT Murrayfield with Chris Paterson, too, which has been great - he's someone I've really looked up to, growing up.
"Everything seems to be happening quickly at the moment and I just need to keep working hard and take the opportunity I've been given with both hands."
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