The Space Gamer (TSG) started out as a digest quarterly publication of the brand new Metagaming Concepts company in 1975. Howard Thompson, the owner of Metagaming, and the first editor of the magazine, stated "The magazine had been planned for after our third or fourth game but circumstances demand we do it now" (after their first game, Stellar Conquest). Initial issues were in a plain-paper digest format. By issue 17, it had grown to a full size bimonthly magazine, printed on slick paper.

When Steve Jackson departed Metagaming to found his own company, he also secured the right to publish The Space Gamer from number 27 on. In the first Steve Jackson Games (SJG) issue Howard Thompson wrote a report on Metagaming and stated "Metagaming's staff won't miss the effort. After the change in ownership Metagaming feels comfortable with the decision; it was the right thing to do." In the same issue, Steve Jackson announced, "TSG is going monthly.... from [number 28 (May 1980)] on, it'll be a monthly magazine." The magazine stayed with SJG for the next five years, during which it was at its most popular and influential. In 1983, the magazine was split into two separate bimonthly magazines published in alternating months: Space Gamer (losing the definite article with the split in Number 64), and Fantasy Gamer; the former concentrating entirely on science fiction, and the latter on fantasy. This arrangement lasted about a year. Fantasy Gamer ran six issues before being folded back into Space Gamer:

"You see, we were churning out magazines - Space Gamer, Fantasy Gamer, Fire & Movement, and Autoduel Quarterly - at the rate of two a month!... We had to find some way to preserve what little sanity we had left. The best way to do this was to merge Space Gamer and Fantasy Gamer.... As it has for the past year, Space Gamer will appear bimonthly, giving us the time to get some games done, as well."

Like Metagaming before it, the effort of producing a magazine became greater than its publisher was willing to bear. The change to bimonthly publication was not enough to allow SJG to focus on new games as they wished, and in 1985, it was announced, "We've sold Space Gamer. We'll still be heavily involved—but SJ Games won't be the publisher any longer. Giving up SG is definitely traumatic... but it gives us the time to do other things, especially GURPS". The magazine had been sold to Diverse Talents, Incorporated (DTI). They initially had it as a section in their own magazine The VIP of Gaming, but it soon became a separate publication again with the previous numbering and format, but with the name Space Gamer/Fantasy Gamer.