Steam controller FAQ Can I use a controller if I don’t have a Steam machine? Yes. It’ll work very well with any version of Steam.
IGN.com The Steam Controller is compatible with both Steam Machine and PCs running Steam. Though the controller can be used to play non-Steam games on PC, functionality is very limited.
IGN.com article Without Steam, if you plug this into one of those devices and run some game that’s not part of Steam, you would only get the most basic functionality. It wouldn’t actually be very valuable as a controlling device.
“It would basically be a mouse with 16 buttons,” Coomer added.