[10] Kasky had just left drama class when the shooting began at Marjory Stoneman Douglas High School in Parkland, Florida on February 14, 2018.

[7] After the shooting, Kasky brought several school friends to his house and with them founded Never Again MSD (#NeverAgain), a student-led gun control advocacy group.

[6][13][14] The group works to create a national movement against gun violence, including an effort to publicize legislators receiving money from the NRA and persuading people not to vote for them.

"[7] Although known as a "theatre kid" with a reputation for being the class clown,[6] Kasky's experience after the shooting was primarily one of anger:[16] Can't sleep.

[17] When later Kasky was accused of being a crisis actor, he replied to CNN's Wolf Blitzer that "if you had seen me in our school's production of 'Fiddler on the Roof,' you would know that nobody would pay me to act for anything.

[21] Later that week, Kasky appeared on The Ellen DeGeneres Show with X González and Jaclyn Corin to discuss their advocacy and march.

"[23] In March 2018, he appeared on the cover of Time magazine along with fellow activists Jaclyn Corin, X Gonzalez, David Hogg, and Alex Wind.

[28][29][30] In March 2018, the Florida Legislature passed a bill titled the Marjory Stoneman Douglas High School Public Safety Act.

It raises the minimum age for buying firearms to 21, establishes waiting periods and background checks, provides a program for the arming of some teachers and the hiring of school police, bans bump stocks, and bars potentially violent or mentally unhealthy people arrested under certain laws from possessing guns.

[33] However, in an interview with Insider in 2022, Kasky has revealed the reason why he left March For Our Lives was because of his ongoing struggle with his mental health which further took a toll on him during the time he was part of the organization.

[37] Kasky endorsed Andrew Yang in the 2020 Democratic Party presidential primaries, claiming to be "very tired of... the same nonsense that's been failing the American people for generations.

"[38] Upon Yang dropping out, Kasky threw his support behind Bernie Sanders, and subsequently endorsed Joe Biden in the general election.