The 28-year-old will sign for Super Rugby side Free State Cheetahs in the summer following an 18-month spell in the Scottish capital. The South African had a slow start to his Edinburgh career after being hampered by an ankle problem following his signing by Michael Bradley in late 2012.
He has formed a key part of the team under Alan Solomons this season, though, making a total of 24 appearances.
However, Van der Westhuizen and wife Bonita have decided to return home with their six-month old daughter. "I've really enjoyed my time at the club, especially in the last couple of months without injury," he said.
"I'm settled in Edinburgh and really enjoy the city but I'm from a very tight-knit family and the chance to be closer to them was one of the biggest, most important reasons - we'll be one hour away instead of 11.
"Scotland will always have a special place for me and I'll be able to look back on a lot of good times. Thanks to everyone for their support during my time here."
Solomons added: "Sakki has done a splendid job for us this year and will continue to do so until the end of the season.
"An opportunity has presented itself back in his home country that suits him and his young family."