The second row partnership is unchanged, with James Ryan packing down alongside Devin Toner.
The 31-year-old will this weekend make his 44th Ireland start under Schmidt, in the Kiwi coach's 54th match at the helm.
Henderson suffered a hamstring injury during the round two win over Italy and sat out the following week's defeat of Wales, a game Schmidt said he could have played in but it would have been a risk.
Ireland are top of the table, five points clear of England, after three wins from three. Injuries to Robbie Henshaw and Chris Farrell mean that Ringrose will step into the no.13 jersey against Scotland despite only returning from a lengthy absence himself, with the Leinster man having only played six games so far this season.
Larmour came off the bench in the win over Italy, and while he looked a bit shaky in defence at times, he looked really exciting in attack with a magnificent break towards the end of the game.
"It's just a case of trying to add some balance, it also adds a bit to our last 20 or 30 minutes of the game".
However, county Tyrone-born Farrell then suffered a season-ending knee injury in training last week, which made Ringrose's inclusion for this weekend's game nearly a certainty.
"There's always concerns about players for different reasons".
"That's something you calculate in, at the same time sometimes you don't have the luxury of a plethora of options".
With rain expected for Saturday's encounter, we may not see the same "Super Rugby" style play from Scotland that they showed in Edinburgh last time out, but one thing is for sure, this Ireland team are not taking this upcoming task lightly.
"If we can create that big mountain for them to climb I think it will be quite hard for them to get back".
"It's a needs-must situation but we have a lot of trust and faith in Garry".
Ireland's replacements bench has four changes as Henderson, Porter, Jordan Larmour and Jordi Murphy take over from Quinn Roux, John Ryan, Fergus McFadden and Jack Conan.