Anthony Sadler, second from left, has now received France's top honour, the Legion of Honour, for his role in thwarting a mass shooting.
French president Francois Hollande pinned the medal on Mr Sadler, US Airman Spencer Stone and National Guardsman Alek Skarlatos after they subdued the gunman as he moved through the train with an assault rifle strapped to his bare chest.
The British businessman, Chris Norman, also jumped into the fray and helped restrain the gunman.
Mr Hollande said the men showed "that faced with terror, we have the power to resist. You also gave a lesson in courage, in will, and thus in hope".
The alleged gunman, identified as 26-year-old Moroccan Ayoub El-Khazzani, is being questioned in custody by French counter-terrorism police outside Paris.
Anthony Sadler's father, also named Anthony, a 57-year-old pastor at Sacramento's Shiloh Baptist Church, told Reuters he was still trying to understand what had happened but that he was "proud" of him.
"We're very, very thankful to God that he was not hurt or killed," he said.
The group were on a European trip when the incident happened by the elder Sadler said: "The trip is over... That's enough. He'll be returning home as soon as possible."
The Americans, wearing polo shirts and khakis against the backdrop of the highly formal presidential palace, appeared slightly overwhelmed as they received France's highest honour.
Mr Hollande said, a "veritable carnage" was avoided.
He said: "Since Friday, the entire world admires your courage, your sangfroid, your spirit of solidarity. This is what allowed you to, with bare hands - your bare hands - to subdue an armed man.
"This must be an example for all, and a source of inspiration."