Need to? No.
However, I think a read of the Wikipedia pages for at least the first two games will help, it is very much a trilogy and the third game ties it off nicely. I played both of the first two before playing The Witcher 3 and it enhanced my experience as well as both being good games especially The Witcher 2. However if youre not on PC theyre not very accessible.
I just decided to change this sig.
Blaaaaaaargh
azuarc