The 22-year-old, who has spent his entire career playing non-League football, has put pen to paper on a two-year contract at Brunton Park.
"He is an exciting one for all of us because he's on the way up," Carlisle manager Greg Abbott told the club's official website.
"We want him to keep that progression going and he's at an age where he's very capable of doing that. He's a very creative player and he's one who we think will make and score goals for us."
Gillies found the net 15 times in 45 Conference appearances last season.