Lewies will be the latest seasoned player to depart the Gallagher Premiership side in recent years, following the likes of Andre Esterhuizen, Wilco Louw, Irne Herbst and Will Collier.
The Pretoria-born lock, 34, began his professional career with the Sharks in 2012, making 63 appearances before moving to the Lions.
He earned a brief international cap, appearing for South Africa for nine minutes in a 55-6 win over Scotland in Gqeberha in June 2014.
Lewies has played 88 times for Quins since joining seven years ago.
In recent seasons, injuries have hampered his game, and before signing his most recent contract in December 2024, Lewies admitted he had contemplated retirement due to ongoing fitness struggles.
The news comes at a challenging time for Quins, who have lost seven of their nine Premiership matches, including a heavy 66-21 defeat to Northampton last weekend and earlier losses to Bristol Bears (40-14) and Sale Sharks (43-17), with a tough Champions Cup clash against the Stormers looming this weekend.
A year after being thrashed at The Stoop, the Stormers head back to London for this weekend's Investec Champions Cup clash sensing a real opportunity against a Harlequins side battling for form.
With a host of players currently sidelined and the depth of the squad being tested, the Stormers took some hard lessons from their Champions Cup clash with Harlequins in London.
The Stormers went down 53-16 in their Investec Champions Cup clash with Harlequins at Twickenham Stoop on Saturday.
Salmaan Moerat makes his return from injury and will captain the Stormers in the Investec Champions Cup clash with Harlequins in London on Saturday.
