The 20-year-old is set to line up in the two-time defending premiers' defence on Saturday against Fremantle.
This time 12 months ago he'd just kicked three goals as part of the Lions' forward line in a preliminary final defeat of Collingwood - just his fifth AFL game.
The Sunshine Coast talent was settling into that role when coach Chris Fagan surprised him with an offer earlier this year.
"I wasn't expecting it ... after playing Sydney, with a few (Lions) out, and they handed it to us," Gallop said.
"He gave me the call and said there's probably not a spot for you up forward this week, how would you like to have a run down back? I was happy to give it a go.
"We all joke about it, me being a defender now. And I'm learning on the go and they've taken me in, but I'm still very close with the forward group as well."
With Hugh McCluggage fit, Gallop was left out of the side that played and lost to Sydney in week one of the finals, but was recalled after Noah Answerth (ankle) was injured in that game.
The easy-going Gallop isn't dismissive of his charmed AFL entry, aware it isn't always so rosy.
"You just stay grateful and look at the bigger picture," he said.
"There's 16 other clubs not in the grand final and no doubt working just as hard as we are.
"So to be a part of two grand finals in two years, I'm just really grateful."
Thousands are expected at the Lions' Springfield training base for Tuesday's open training, before the side flies to Melbourne on Wednesday.
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