First of all: If you want a game here, you should buy it here...

It is possible for The Witcher 1 and 2 but not for the third.

Now you want links to where it can be done. I looked but someone else was faster.

You might be able to reclaim the first two games on GOG, if you have some kind of CD or product key, by using GOG's Witcher Backup page. I don't know where you would find this key in your Steam version, but the page says "available to gamers who bought either of these games for PC or Mac at any other store in the world", so I guess it must be somewhere in the Steam version as well.

I fear Witcher 3 is not part of this offer so far though, so unless they do a promo of sorts for that, you won't be able to get a GOG version without buying it.

EDIT: Does Witcher 3 use Steamworks DRM, btw? I would assume they'd make it DRM-free on Steam as well. (If not that would be low.)

Buy it again, it's at 70% right now so there's no excuse not to... CD Projekt Red is one of the few big AAA developers left that makes really gog games with gog stories and they deserve every money they can get.

Don't encourage people to waste their money like that.

Pal, you've got the games. Just install them and enjoy them. Where you get them from is completely irrelevant.

He seemed to really wanted a copy on GOG too so why not? Also, considering the amount of hour you get in W3 it's nothing. :D

$15 is cheap if you don't own the game yet, but very expensive for a library icon and an alternative installer that you might not need at all. OP also said "without paying".

In the end we give him advice, and it's up to him what he want to do or not (or she). ;)

Alright boys let's relax here.
Thanks for the help everyone, I understood that it is not possible ATM to convert The Witcher 3 from Steam to GOG, but I now do have TW1 and TW2 on my GOG library.
It kinda sucks to have to pay again so I probably won't bother just for the DRM free service. But still thanks for the advice, as I primarily just wanted to know if it was possible.

There is gog connect which did give you a copy of a very select few games, has pretty much died though. And there was a redeem from cd for a couple. The problem is twofold though, if gog gives steam users free copies it doesn’t make money, and thus goes out of business. Likewise, if publishers give free games out, then they lose revenue.

Essentially, when you purchase a digital product, you are buying a license to use that product inline with the agreement you made at purchase. So if you brought on steam, you have a license agreement with steam. Only by a publisher granting you another license on another platform can you legally own it. I don’t know of any store which alllows transfer of digital licenses freely and legally.