The Glasgow centre says it was a "shock" to be asked to skipper Scotland but he believes his experience leading the URC champions this season has helped him grow as a player.
"Gregor told me and Luke Crosbie together that we'd be co-captaining when we first came into camp," McDowall said.
"It was a bit of a shock, I was a bit overwhelmed. I was straight on the phone to my dad and he's coming out for the game on Saturday.
"He was always planning to come to one game, and when he heard I was going to be co-captain, he was like 'that's the one'. It's a special day for my family. He's played a massive role in my career so I'm glad I get to share the day with him.
"Being part of the leadership group at Glasgow has been massive for me. Just having the confidence to put my thoughts forward."