The former Watford trainee, who has made only a handful of appearances for the Robins, went on as a first-half substitute for the injured David Bird; scored his second goal of the season and was then sent off midway through the second half.
Gill was booked for over-celebrating his goal and was then given a second yellow card by referee Phil Crossley for tripping Swindon defender Yinka Casal in the 69th minute.
Seven minutes earlier, Gill scored his second goal in a week after new loan signing Barry Hayles showed admirable strength in the penalty area before laying the ball off for Gill to score from a 45 degree angle 12 yards out.
After the sending-off Swindon were unable to impose themselves and Cheltenham added a second ten minutes from time when Jennison Myrie-Williams, another player signed on loan this week, met an Alex Russell cross with a bullet header.
The game had been evenly contested until that first goal with Swindon probably shading the contest in terms of quality of chances.
They created the best openings of a scrappy first half with winger Jon-Paul McGovern delivering some fine crosses from the right-hand side.
McGovern set up defender Sean Morrison for a powerful header that Cheltenham goalkeeper Shane Higgs pushed aside.
Higgs had to be at his best again shortly before the break when a McGovern cross found Simon Cox, who laid it back for midfielder Michael Timlin to strike at goal.
Cheltenham went close with a Craig Armstrong drive from distance and a deflected Ashley Vincent shot that just cleared the crossbar.
After the break, Swindon began the second half very strongly and exerted a lot of pressure on the Cheltenham goal. Simon Cox should have scored when he darted onto another McGovern cross at close range, but his shot cleared the crossbar.
The game turned on the substitution of Paul Connor for Ashley Vincent that gave Cheltenham and extra man in attack. The first goal and subsequent drama followed shortly after that.