Skarlatos joined the Oregon Army National Guard in 2012, achieving the rank of Specialist. He completed a nine-month deployment in Afghanistan with the National Guard’s 186th Infantry Regiment, 41st Infantry Brigade Combat Team in 2015. The acting adjutant general of Oregon Guard referred to Skarlatos as “a true citizen soldier who displayed the courage each of us would hope to find in ourselves.” A month prior to the terrorist event on the high-speed train in France, Skarlatos had reenlisted for an additional two-years. He left the military service in November 2017.

On August 21, 2015, Skarlatos and two friends from his childhood home of Carmichael, California, were traveling together on Thalys train 9364 from Amsterdam bound to Paris via Brussels during a vacation in Europe. He was recently back from serving in Afghanistan, and they had been traveling in Germany and the Netherlands. A 25-year-old Moroccan, Ayoub El-Khazzani, exited the toilet in train car No. 12, armed with an AKM assault rifle, a Luger pistol, a box knife, a jar of gasoline and was carrying magazines holding 270 rounds of ammunition for the assault rifle in a rucksack. Two people, a Frenchman, “Damien A.,” and 51-year-old Mark Moogalian, an American expatriate living in Paris, tried to stop the gunman. Moogalian wrested the rifle from him, but he was shot with the Luger as he tried to protect his wife. Skarlatos’ friend, 23-year-old Spencer Stone, ran toward and attacked the gunman next and was slashed while trying to subdue him. Arriving next to the struggle, Skarlatos picked up the assailant’s rifle, beating him in the head with its muzzle, and 62-year-old Briton Chris Norman also helped subdue the gunman. Though badly cut, Stone strangled him until he was unconscious. The terrorist was tied up and then Stone, who had some military medical training, delivered lifesaving assistance to Moogalian by pressing down on an exposed, bleeding artery.

After the attack, on August 22, 2015, Skarlatos and his friends received international attention for their actions in thwarting the attack. French president François Hollande awarded Skarlatos, his friends Spencer Stone and Anthony Sadler, as well as British businessman Chris Norman, France’s highest decoration, Knights of the Legion of Honour (Chevaliers de la Légion d’honneur). Hollande said the men “faced [off] with terror” and that they “gave us a lesson in courage, in will, and therefore in hope”. French Interior Minister Bernard Cazeneuve praised them for their bravery, as well as British Prime Minister David Cameron.

In October 2016, it was announced that Skarlatos, Spencer Stone and Anthony Sadler would make an appearance on Who Wants to Be a Millionaire as a part of the show’s special “Hometown Heroes” week which would premiere on October 31, 2016.

In July 2017, it was announced that Clint Eastwood would direct the upcoming biographical film titled after Stone, Skarlatos and Sadler’s memoir, starring them, along with actresses Jenna Fischer and Judy Greer. Filming began on July 11, 2017. The film was released in the United States on February 9, 2018. The film received a generally negative reception from critics, who were largely critical of the acting by the three leads.

Skarlatos ran for Douglas County Commissioner in his home state of Oregon in the 2018 midterm elections, but he lost to businessman Tom Kress. Skarlatos said on election night that his opponent’s 2% lead made the race still incredibly close, continuing, “We have a lot of great people and I think we’re going to have a better response from the exterior of the county, so I’m still very optimistic.” He wasn’t surprised by Kress’s lead, saying, “He’s outspending us by 2 to 1 and took his campaign really negative.”

In September 2018, Skarlatos became an honorary naturalized French citizen, along with Stone and Sadler. A naturalization ceremony was held in Sacramento in January 2019. Skarlatos was raised a Presbyterian but now belongs to a Lutheran church.

In 2019, Skarlatos announced that he was running as a candidate in the 2020 elections to represent Oregon’s 4th congressional district in the United States House of Representatives as a Republican.

Skarlatos won the Republican primary, on May 19, 2020, defeating Nigeria-born Nelson Ijih. He lost to incumbent Democratic congressman Peter DeFazio in the 2020 November general election by over 25 thousand votes.