The rally on the US Capitol saw signs reading "Stop mass surveillance," "Thank you, Edward Snowden" and "No NSA mass spying."
The marchers included a diverse range of interests and ideologies, including right-leaning, libertarian, left-leaning groups.
The more than 100 public advocacy groups organizing the event, including the the Electronic Frontier Foundation and the Koch brothers' FreedomWorks, will deliver a petition to Congress on Saturday
The Washington Post reported that the tech community was out in full force during the rally.
“This is probably the defining issue of a young generation of technologists,” said software developer Matt Simons of ThoughtWorks, which helped sponsor the event.
“If you’re not coming out on the right side of history, you’re in the wrong industry.”
The march, which lauded libertarian and anti-spying figures like journalist Glenn Greenwald, former NSA contractor Edward Snowden and Republican politician Rand Paul, was timed to happen on the 12th anniversary of the signing of the Patriot Act, the law used to justify the espionage programs.
The NSA spying controversy erupted in June after Snowden leaked top secret documents to the Guardian and Washington Post newspapers revealing massive surveillance programs.
Near weekly revelations have dominated headlines and sparked debate but US public outcry has been largely reserved to social media debates and newspapers. This is the first major US demonstration against the spying programs, while a similar rally was held in Berlin in July.