Outcast, Master of Orion, and Master of Magic are the first titles named in the new deal, which should begin showing up on the service in April.
"This is a great step forward for GOG.com and DRM-free digital distribution," said Marcin Iwinski, co-founder of CD Projekt and GOG.com. "This deal is really just the first step in what we expect will be a long and fruitful relationship. Atari has a tremendous number of cult classics within their grasp, and we hope to sign these in a near future!"
GOG is also giving away 10 free games through Twitter to commemorate the announcement. Users must "Re-Tweet" the message to be entered.