Tonks, who went to school in Nottingham and university in Leicester, qualifies to play for Scotland through his grandmother, who is from Ayrshire.
The 22-year-old, who plays predominantly at full-back, started out at Leicester Tigers before joining Northampton and will end a two-year stay at Franklin's Gardens by joining the Gunners.
And after moving north of the border for the start of next season, Tonks could well be in contention for next season's RBS 6 Nations.
"Edinburgh play really good, attacking style of running rugby," said Tonks, who will now play his home games at Murrayfield.
It's something I noticed when I played against them last season. They have the ability to take teams apart at speed and being part of that is something I'm very excited about.
"To play at Murrayfield will also be fantastic.
"It's an impressive international arena with incredible training facilities so this move presents a pretty awesome opportunity for me to develop as a player and be part of something special with Edinburgh."