His siblings were at the school during the Stoneman Douglas High School shooting in 2018 while his brother filmed from inside the school. Deitsch was buying cake for his sister because it was her birthday that day when he received a call from his mother saying there was an incident at the school. After the shooting, Deitsch, along with his siblings and Emma Gonzalez and David Hogg, brainstormed to come with a grassroots platform which eventually became March For Our Lives and Never Again MSD, the former in which he became director of strategy and ran day-to-day operations with Jaclyn Corin. Since then, Deitsch has dedicated his time to work on gun control advocacy in his own right and on behalf of Never Again MSD. In November 2018, he travelled to Cape Town, South Africa, to accept the International Children's Peace Prize on behalf of March For Our Lives, along with his brother, Gonzalez, Hogg and Corin. He appeared on "Good Morning America" and "The Daily Show with Trevor Noah" to talk about gun violence and also co-authored a book with March For Our Lives titled "Glimmer of Hope: How Tragedy Sparked a Movement" in October 2018. Deitsch appeared in the 2020 documentary film "Parkland Rising" about the shooting and subsequent student activism. In 2020, Deitsch joined Bernie Sanders's campaign for president of the United States as a gun violence prevention advisor and helped develop a gun violence prevention platform for the campaign. In an announcement, he commented: "America's gun violence epidemic is a public health crisis that requires dedicated organizing. The Military Industrial Complex has tainted our health across America and abroad, I am proud of Senator Sanders’ growth and commitment to ending gun violence, and we won't win this fight for all of our safety unless we organize at a historic level. And that's what we are setting out to do with this effort.”