The new agreements will see Golby, 21, and Harwood, 22, remain in Brisbane until at least the end of the 2015 season.
The pair join Matthew Leuenberger, Daniel Rich and Dayne Zorko, who have all extended their contracts with the Lions during the past few months.
Lions general manager of football operations Dean Warren said Golby and Harwood were two of the most talented young defenders at the club.
"Mitch and Ryan’s commitment demonstrates the confidence our players have in both our football program and our future," he said.
Golby was drafted by the Lions at the end of 2009 midway through his rehabilitation from a knee reconstruction and was a NAB AFL Rising Star nominee in 2012 before he was sidelined from round 14 onwards with a stress fracture in his foot.
He has emerged as one of the Lions' most important players this season, with his clever ball use and run from the back half a nice replacement for the retired Josh Drummond.
Harwood was selected with pick number 47 at the 2010 NAB AFL Draft and has played 37 career games including eight in 2013.
Lions coach Michael Voss transformed Harwood from a bullocking midfielder to a running half-back midway through last season.
Michael Whiting is a reporter for AFL Media. You can follow him on Twitter: @AFL_mikewhiting
