An early penalty followed by two-second half strikes gave Saddlers a deserved win and made it nine wins from the last 13 for the impressive visitors, who kept their play-off hopes alive.
Walsall had the best possible start when they were awarded a penalty inside three minutes after Carlisle goalkeeper Mark Gillespie's rash challenge resulted in a foul on James Chambers.
Grigg hammered home the spot kick giving Gillespie no chance of saving as it flew past the diving keeper's right hand.
Saddlers' pace and accurate passing had Carlisle's midfield chasing shadows at times and Grigg almost had a second, sliding in at the far post and just failing to connect with Craig Westcarr's cross.
Liam Noble and Rory Loy tried to gain a foothold in the game for Carlisle with shots from outside the box which went close, but again it was Walsall who carried the greater threat, Sam Mantom forcing Gillespie to beat away a powerful drive from 20 yards.
Febian Brandy and Westcarr continued to test the home defence and it took a fine Gillespie save to deny the latter after a 40-yard run, although Carlisle forward Lee Miller's header was kept out by an even better Aaran McCarey stop at the other end.
Saddlers doubled their lead in the 66th minute when Grigg worked himself some shooting space just inside the area to slot a low shot just inside the post.
And the Northern Ireland international put the result beyond doubt in the 86th minute when he fired home from inside the area after a couple of shots had been blocked by desperate Carlisle defending.