Ipswich-born Wilkins was in the Saints Academy and was part of the squad that won the Premiership’s Under-18 Academy League in the 2013/14 season, alongside the likes of Harry Mallinder, George Furbank, Lewis Ludlam, Rory Hutchinson and James Fish.
But he opted to head off to France to join Montferrand and had spells with Clermont Auvergne and Béziers, where he has made more than 50 appearances in ProD2.
But Wilkins, who stands at 6ft 4in tall and can play at lock as well as in the back row, believes now is the time to return home.
“I’m absolutely delighted to be returning home and to get my opportunity with Northampton,” said the 24-year-old, who will switch to Saints this summer.
“I grew up playing at Franklin’s Gardens, so I understand the culture and tradition of the club, the special atmosphere inside the stadium on matchday, and how important Saints are to the people of the town.
“It’s been fantastic to see some of the lads I played alongside in the Academy take their opportunities and really kick on in recent years - I hope when I return to the club, I can do the same and make more memories with them.
“The squad is already filled with talent and I can’t wait to arrive and try to develop further as a player under a really impressive group of coaches.”
Saints signed No.8 Shaun Adendorff from ProD2’s Aurillac last summer, and he has already proved to be something of a success story, scoring four tries in his past three games.
And Saints boss Chris Boyd is confident Wilkins could prove to be another hidden gem when given an opportunity in the top-flight of English rugby.
Boyd said: “Karl fits our recruitment model of young, high-potential and English perfectly.
“We want to continue to build a squad with a backbone of local players, and while Karl has taken the road less travelled to get here, he is desperate to pull on a black, green and gold jersey again.
“He is someone who can play both lock and in the back row, so Karl’s a versatile player and a great fit for our pack.
"I’m looking forward to seeing how far he can go within our set-up here at Franklin’s Gardens.”