The 33-year-old, whose previous clubs also include Derry City and Tranmere Rovers, played 114 times for Rovers.
"It is great to be involved with such a great club as Crusaders - I hope I can bring more success to everyone here on the Shore Road," said McChrystal.
"They have shown over the last lot of years how good a team they are in winning Premierships and other cups."
McChrystal is the latest summer signing for the Crues after the arrival of Brian Jensen, Sean Ward, Jamie Glackin and Mark McAllister.
"I am extremely pleased to get Mark to the club," said Seaview boss Stephen Baxter.
"His pedigree is exactly what we need to join us and he will bring a vast amount of experience as we go into the new season."
Crusaders have brought in former Bristol Rovers defender Mark McChrystal on a one-year deal.