Smith, one of the best batsmen of his generation, was a late candidate to replace David Warner after the veteran opener retired from the format in the wake of Australia's sweep of their three-match series against Pakistan over the New Year.
His move up the order makes way for Green to slot in and play his 25th test in the position where he has been a prolific run-scorer for Western Australia.
"We were pretty open that we thought Cam Green was in our top six batters and really all there was to iron out was the details around the order," captain Cummins told reporters in Adelaide.
"It wasn't until around then that we started chatting seriously to (Smith) and found out just how keen he was ...
"It all made sense to get Smithy into a position that he'd love to bat in, and Green into a spot (he) knows pretty well."
With all-rounders Green and Mitch Marsh in the team, Cummins has plenty of bowling options to take the pressure off him and fellow quicks Josh Hazlewood and Mitch Starc as they all play their fourth test of the home summer.
West Indies are without their best all-rounders Jason Holder and Kyle Mayers with the duo having preferred to play in lucrative Twenty20 leagues.
Skipper Kraigg Brathwaite also named his team on Tuesday and confirmed that Kavem Hodge and all-rounder Justin Greaves would make their test debuts in the middle order with quick Shamar Joseph also winning his first cap.
"I'm expecting a lot of fight from the guys, obviously guys relatively new to test cricket and they've got to show the world their worth," said Brathwaite.
"We've got to work extremely hard and we have to believe in ourselves."
Once the most feared of tourists when their famed pacemen terrorised batsmen on Australia's hard decks, West Indies have not tasted victory Down Under in 16 matches going back to their last win in Perth in 1997.
Australia won a day-night test by 419 runs at Adelaide in December 2022 -- the biggest win by runs in test history -- as they swept West Indies in a two-match series. The second test this year is a pink ball test in Brisbane starting on January 25th.
