The 28-year-old joined Saints back in 2016 and has gone on to make 51 appearances in the Black, Green and Gold while scoring seven tries in the process.
With a chance to join the Lions in Super Rugby, Groom has decided to make a return to his homeland and has thanked Northampton and its supporters for the time he has spent at Franklin's Gardens.
"I have loved the opportunity to come over to the UK and play for such a great Club in Northampton Saints," he told the club's official website.
"But the time has come for me to return to South Africa. An opportunity has come up to return home, and I am grateful to the Club for allowing me to head back early to try and make my mark.
"The Northampton Saints, the supporters and the local community will always have a special place in my heart. Playing at Franklin's Gardens in front of these fans has been an honour, and I will cherish every moment of my time here.
"I want to thank my teammates, coaches and the friends that I have made since moving, and I wish them all the best for the future. I leave Northampton a better man with a heavy heart, but I have no doubt the Club will be flying in no time - come on you Saints!"