The Glasgow centre will lead his country against Fiji and admits it is a moment he and his family will cherish.
"I'm really excited. I've been here a couple of times before and it's been really fun. It's a massive honour for me and my family so I'm really excited to get another shot at it.
"This is the first Tier 1 side so I'm really looking forward to getting another chance to do it, particularly at Murrayfield in the sunshine. I know it's technically an away game, but I'm really excited for it."
Head coach Gregor Townsend has named a much-changed side, making 14 alterations from last weekend's clash with South Africa, but has brushed aside any concerns over the inexperience of the starting XV.
McDowall says settling back into the team and taking on the captaincy has been straightforward, crediting the strength of the squad and the support of Tuipulotu, who starts on the bench.
"We're such a tight-knit group and we've come together so well in the last year.
"Sione mentioned today how much we've grown as a group in the last year. A lot of the boys that are playing tomorrow maybe haven't had as many opportunities this season or on this tour.
"You don't go and try and do something individual on your own, because that's what Fiji want, us to go in and try and match their style of play, of free-flowing offloads.
"I'll just be focused on my role tomorrow. I don't need to do anything too much different."
On sharing leadership responsibilities with Tuipulotu, McDowall added: "He's one of my good mates. He's a great leader.
"It makes it a bit easier knowing he's there and he can lead some of the huddles and do some of the speaking as well. He's such a pivotal figure for this team and it does make it a lot easier."
Saturday's match is Scotland's final outing of a long season, and McDowall believes it is important to finish the campaign on a positive note after victory over Argentina and an encouraging performance against South Africa.
"You don't want to leave a sour taste in your mouth for the end of the season.
"It's been such a strong season for a lot of the boys, for club and country.
"You want to finish it on a high, especially with over 50,000 people, mainly Scotland fans, having bought tickets to come here and watch.
"You want to put on a good performance for them. You represent the country and you never want to let that opportunity go by and not give it your all."