More than 800 sister protests were planned nationwide and abroad, with solidarity events taking place in Edinburgh, London, Geneva, Sydney and Tokyo.
As events began to draw to a close on the US east coast, they continued on the west, including a major demonstration in Los Angeles.
What happened in Washington?
Huge crowds – including a high proportion of young people and children – gathered along Pennsylvania Avenue, with placards reading “Protect kids not guns” and “Am I next?”.
Singers Ariana Grande, Miley Cyrus and Lin-Manuel Miranda, the man behind hit musical Hamilton, performed on a stage erected in front of the US Capitol building.
The music was interspersed with speeches from impassioned youth leaders.
“We will continue to fight for our dead friends,” said speaker Delaney Tarr, a Parkland student.
Some came from children who are just 11 years old, including Naomi Wadler, from Virginia, who spoke “to represent African-American girls whose stories don’t make the front page of every national newspaper”.