Three defeats on the spin had seen the Cumbrians drop to mid-table but Gall's wonder strike brought relief all around at Brunton Park.
Drifting in from the left wing, the Welsh striker evaded three challenges on the edge of the penalty area before curling a perfectly angled shot inside the far post.
It was tough luck for Tranmere who had already hit the post through Kevin Ellison before the forward was forced off with an injury early on.
Man of the match Chris Shuker skipped past his marker, Zigor Aranalde, and laid on a perfect cross for Ellison, who could only stab it onto the post from eight yards out.
Substitute Steve Davies blasted wide for Rovers, but in truth the visitors deserved little from their first-half showing.
Just four minutes into the second half, Tranmere midfielder John Mullin joined Ellison on the injured list and his replacement, Danny Harrison, was lucky to stay on the pitch more than a few seconds after dragging back Simon Hackney as he ran in on goal.
Harrison escaped with a booking and Peter Murphy's free-kick from the edge of the area was well saved by Gavin Ward.
Shuker, tormenting Aranalde yet again, jinked past the Basque full-back but could only offer a poor shot with just the goalkeeper to beat.
By now Tranmere were camped in the Carlisle half and Shuker twice had the ball in the net direct from corners, but the referee blew for a foul on goalkeeper Keiren Westwood on both occasions.
The referee was again in Tranmere's sights when he failed to give a penalty for a clear handball by home skipper Kevin Gray in the 81st minute.
Carlisle's defence held firm late on, but the visitors failed to create any clear-cut chances as they lost their second game in a row.