Cobus Reinach will leave the Northampton Saints at the end of the 2019-20 European season.
The 29-year-old scrumhalf has played 70 matches for Saints since joining the club in 2017, scoring 29 tries.
'I love playing for Saints and living in Northamptonshire,' Reinach said. 'We have a fantastic group of coaches and staff, and an exciting squad that I believe can challenge for the major honours, so this has not been an easy decision for me to make.
'I'd like to thank everyone for making the last three seasons so memorable; I'll be sad to leave some great friends and teammates.
'Saints will always have a special place in my heart and I look forward to giving everything I've got to make sure we finish the season with some silverware.'
Reinach is reportedly set to join French club Montpellier.