The 28 year-old played over 100 games at Brunton Park but found himself out of contract at the end of last season.
Collin played over 200 games for non-league Workington before moving to Carlisle and was also previously on the books of Newcastle United.
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.
Boss Evans added: "We identified him in February as a potential target, and there was interest from two established League One clubs. He’s six feet four, kicks it well, he’s strong and has a big presence and has a real pedigree."