The English actor was perhaps best known for his recurring role as Ethan Rayne in Joss Whedon's Buffy the Vampire Slayer.
His death was announced on his official Facebook page earlier today (February 5).
A post read: "It is with great regret that we at Robin's official fansite have to announce his sudden and unexpected passing.
"He was an amazing and wonderful man and we are all heartbroken. Please raise a glass and toast to the life and career of the wonderful Robin Sachs."
Further details about his death have yet to be confirmed.
Sachs portrayed characters in several science fiction franchises, including roles in Babylon 5, Star Trek: Voyager and Torchwood.
He played the main villain General Roth'h'ar Sarris in 1999 comedy Galaxy Quest, and also provided the voice for Zaeed Massani in the video games Mass Effect 2 and Mass Effect 3.
Robin Sachs appeared in four episodes across three different seasons in Buffy the Vampire Slayer from 1997 to 2000.