Jumping early from a significant distance behind the front of the race, Ewan kept his momentum all the way to the line, beating Elia Viviani (Deceuninck-QuickStep) and Dylan Groenewegen (Jumbo-Visma) comfortably.
"It was such a big dream to win one stage and now I've won two, I can't believe it," he said.
Ewan was well-positioned by his Soudal Lotto team mates going into the final kilometre but appeared swamped by the acceleration of Deceuninck-QuickStep. But being out of position at this point was an outcome he planned for prior to the stage.
"We were too far forward," said Ewan. "I had Jasper (De Buyst) on the front with Dylan (Groenewegen) on the wheel with one kilometre to go. We weren't in an ideal situation.
"QuickStep came past and I lost a few more positions than I wanted to. I looked at this finish at the start of the day and I played all the scenarios in my head.
"One of the scenarios was if I was too far back, I lay off the wheel through that roundabout and just went full gas and luckily it was enough speed to come around."
The 25-year-old speedster said his wife Ryann and baby daughter Lily spurred him to victory at the Stage 16 finish in Nîmes.
"This one was extra special because I had my daughter and my wife waiting for me. I'm so happy I could win for them."
"I really needed that motivation because I was really struggling with the heat. Halfway through the race I was almost going to tell Max (Monfort) to come off the front because I was suffering so much but once the adrenaline kicked in for the final, I had my eye on the prize and I had the legs in the end."
SBS' Sophie Smith asked how it felt to have his second stage victory given he waited so long to get a dance at the Tour.
"It means a lot. In a way it proves that I could've been here already. I'm so happy to win two on my debut."
Today's 177km stage around Nîmes was mostly about riders trying their best to stay cool in the 40 degrees celsius heat with ice and water throughout the stage.
Paul Ourselin (Total Direct Energie), Stephane Rossetto (Cofidis), Lukasz Wisniowski (CCC), Alexis Gougeard (AG2R La Mondiale) and Lars Bak (Dimension Data) formed the early breakaway, but there was little action as Tony Martin (Jumbo-Visma) and Monfort kept them pegged.
The catch was made within the final three kilometres as the teams proceeded to fight for stage honours.
It was a mostly uneventful stage for the general classification, although Jakob Fuglsang (Astana) crashed out of the race with a suspected fractured hand.
Geraint Thomas also took a tumble some 129kms from the finish caused by what the Welshman said was the gears jumping. It's the defending champion's third crash at this year's race coming undone in Stages 1 and 8.
But he said after the stage it was "all good, just a bit of blood."