The left-arm paceman, who has 205 Test wickets at an average of 30.93, was omitted from the touring party for the 3-0 series defeat to England this summer due to inconsistent performances, particularly away from home, over the past two years.
These signs of a return to form, combined with several injuries to other Aussie seam options, has resulted in pleas for Johnson to be recalled, and Gillespie, now coach of Yorkshire County Cricket Club, feels that the 31-year-old could feature prominently for the Ashes rematch down under.
"He could play a big role," Gillespie told BBC Sport. "He has the desire and drive to reignite his Test career. "I spoke to him the other night and he is leaving no stone unturned, working really hard.
"The Australian support staff are absolutely thrilled with how he has been coming along. He's reverted back to his longer run-up. He's running in slightly differently, his arms are not swinging as much and he is a bit more compact and streamlined running in to bowl.
"That is getting him into a really good position at the crease to unleash the ball. I think he is in a pretty good place and that is improving his consistency."
Gillespie took 259 wickets in 71 Tests for Australia and also made the highest ever score by a nightwatchman when he amassed an unbeaten 201 against Bangladesh in 2006.