The 6ft 7in (2.01m) forward, 22, has played 86 times for Saracens, who have been relegated to the Championship.

Isiekwe, who can also play in the back row, won the most recent of his three Test caps in June 2018.

"I know that he'll be 100% committed to the club and immerse himself in our culture," said Saints boss Chris Boyd.

"Not only will he add value to our squad, but I hope we can help him improve and reach his goal of playing regular international rugby."

Isiekwe played in Saracens' victorious 2018 and 2019 Premiership finals, as well as their Champions Cup triumph last season.

Speaking about his new contract with the London side, he said: "I'm over the moon to commit my future long-term."