Around 100 people from Newtown, Conn., were expected at the rally, which was organized in response to the deadly mass shooting there last month.
Others had come from all over the US, organizers said. Photos showed marchers carrying signs with pictures of victims of gun violence, while others held banners reading: "Protect children, not guns."
Lawmakers and shooting survivors addressed the crowd in front of the Washington Monument. Education Secretary Arne Duncan told protesters: "We must act, we must act, we must act."
According to the organizers' mission statement, they support President Barack Obama's proposals to have Congress ban assault weapons and high-capacity ammunition magazines, and require background checks for all gun customers.
On top of that, they're calling for a 28-day waiting period and mandatory safety training before anyone can buy a firearm, as well as a ban on bullets that shatter in the body.
Obama unveiled his package of executive and legislative measures to help tackle gun violence 10 days ago, and Vice President Joe Biden has since been leading efforts to sell them to the American public.
They face stiff opposition from advocates of gun rights: last weekend, Reuters reported, campaigners held rallies across the US opposing stricter weapons laws.
Saturday's march, in contrast, was co-sponsored by One Million Moms for Gun Control, a group which has helped organize similar events from San Francisco to New York.