Paul McCartney Joins March for Our Lives, Remembers John Lennon

"One of my best friends was killed by gun violence right around here, so it's important to me not just to march today but to take action tomorrow and to have these people to have their voices heard," McCartney told CNN's Jason Carroll.

Caroll asked McCartney what he hoped could be achieved by the rally, to which McCartney opened his jacket to emphasize the message on his shirt, which read, "We can end gun violence." McCartney said he wasn't sure whether gun violence could be ended on the legislative level, but said that what citizens can do is march.

The former Beatle was joined by his wife Nancy Shevell at the rally blocks away from the Dakota Building, outside of which John Lennon was shot in 1980.

In McCartney's native England, it's significantly more difficult for private citizens to own guns, a result of a 1996 mass shooting in Dunblane, Scotland, in which a gunman killed 16 children and a teacher. After the shooting, all handguns were banned from private ownership, with over 162,000 being surrendered in a gun amnesty. Only one mass shooting has taken place in the U.K. since, in 2010.

Several other celebrities expressed their support for the cause Saturday and attended rallies in their cities. Demi Lovato performed at the Washington, D.C., rally, and others like Kim Kardashian West, Liev Schreiber and Nick Offerman posted about their intention to rally.