The 29-year-old will move to the Twickenham Stoop at the end of the season in a significant coup for Quins who currently sit second-bottom of the league after only three league wins from 12 matches this season.
Furbank was named captain of Northampton at the beginning of last season but fractured his arm which caused him to miss much of the 2024-25 campaign.
This season he has made 11 starts in total for the Prem leaders, scoring against Sale Sharks at home in the league, as well as against Saracens in the Prem Rugby Cup and he was influential in Saints' 49-41 Champions Cup victory over Castres which secured a quarter-final tie against Bath on Friday.
At international level, Furbank made his England debut under Eddie Jones, starting against France in Paris during the 2020 Six Nations title-winning campaign.
He scored his first try against Scotland in the 2024 edition before a second-half try against Ireland helped earn England a memorable 23-22 victory at Twickenham.
In total, Furbank has 14 international caps for England and leaves Northampton after a decade at the club.
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"George also has a strong ambition to return to the Test arena with England heading into a World Cup year, and we're really looking forward to seeing the impact he'll make here at The Stoop."
Furbank leaves Franklin's Gardens a Prem title winner as Saints picked up the league championship in 2023-24 following a 25-21 victory against Bath in the final.
That season, Furbank scored seven tries and kicked 39 points with the boot in a career-best campaign so far, and he has the opportunity to lift the trophy as captain with Saints in June as they currently sit top of the Prem standings by one point.
"Winning the Prem title with Saints will always be one of the most special days of my life, and something I'll carry with me forever," Furbank told Northampton's website., external
"This was a really difficult decision to make. I've given everything to Saints over the last 10 years, and from now until the end of the season my focus is on doing everything I can to help us finish on a high note."
