Gillingham will play Millwall in a pre-season friendly at MEMS Priestfield Stadium on Tuesday July 21.
Kick-off is set for 7pm.
This fixture will follow an away game against Dover Athletic on Tuesday July 14, and Charlton's visit to ME7 on Saturday July 18.
Millwall, now under the management of Alex Neil, secured a Championship play-off place last season but were defeated by Hull City over two legs.
Ticket details ahead of the fixture will follow in due course.
