The 28 year-old played over 100 games at Brunton Park but his contract was not renewed at the end of last season.
Collin started out with Workington before moving to Carlisle and was also previously on the books of Newcastle, Oldham and Doncaster.
He will compete for the number one spot with Scott Shearer.
“There was a bit of interest from League One and the SPL but I’ve chosen to come here because it’s a club on the up with a great setup at the training ground and the stadium. The location and the fanbase are excellent,” Adam exclusively told Millers Player.
More to follow.