The Lions sent pick 14 in the 2007 NAB AFL Draft to Melbourne to acquire Johnstone ahead of the 2008 season and he managed 49 games in three years at the club.
Johnstone struggled for form and fitness in his stint with the Lions and was dropped on several occasions over the past two seasons.
The former No.1 draft pick leaves the Lions with 209 AFL games to his credit and at 30 years of age looks set to remain on that figure.
Also departing the club are Albert Proud and ruck project Bart McCulloch, while rookies Sean Yoshiura and Broc McCauley have not been offered new contracts.
Proud took a leave of absence from the club back in May to deal with personal issues, but returned to play five of the Lions' last six games.
National talent manager Rob Kerr thanked the players for their efforts and is now looking forward to the draft where his club will be a prominent player.
"Today's announcement allows the club to go to the 2011 NAB AFL Draft with picks 5, 25, 27 and 31, and the option of using two compensation picks for the end of round one," Kerr said.
"The nature of footy is that there will always be players coming and going at the end of the season - we are looking to 2011 with a new vision for the team, and we believe that the changes made will facilitate this."
Kerr goes into the draft armed with those picks thanks to some trade week wheeling and dealing that saw Jared Brennan join Michael Riscitelli at Gold Coast and Justin Sherman move to the Bulldogs.
Claye Beams, brother of Collingwood's Dayne, has been elevated from the rookie list to the primary list.
