Though the court recognized that O'Brien's conduct was expressive as a protest against the Vietnam War, it considered the law justified by a significant government interest unrelated to the suppression of speech and was tailored towards that end.

Though the O'Brien test has rarely invalidated laws that the court has found to be "content neutral", it has given those engaging in expressive conduct—from wearing of black armbands to burning of flags— an additional tool to invoke against prohibitions.

[a] On the morning of March 31, 1966, David Paul O'Brien and three companions burned their draft cards on the steps of the South Boston Courthouse, in front of a crowd that happened to include several FBI agents.

Chief Justice Earl Warren's decision for the court rejected O'Brien's argument that the 1965 amendment to § 462(b)(3) was only passed to stifle the speech of anti-war protesters.

The law did not restrict speech on its face, but instead only addressed conduct that was not necessarily expressive, and applied without regard to whether the draft card was destroyed in private or before an audience.

And fourth, the court saw "no alternative means" by which the government could ensure that draft cards would continue to be available than a law that prohibited their willful destruction.

[10] Harlan wished to extend First Amendment protection to instances in which, though the majority's test was satisfied, the regulation at issue additionally had "the effect of entirely preventing a 'speaker' from reaching a significant audience with whom he could not otherwise lawfully communicate".

This was adopted in later cases by the court as an additional prong of the O'Brien test, that the regulation must leave (as phrased in later decisions) "ample alternative channels" of communication.

Though the court has not revisited this specific issue, the court ruled for other anti-war protesters very soon after O'Brien in Tinker v. Des Moines Independent Community School District,[13] which involved public school students who were suspended for wearing black armbands, and Cohen v. California, in which a man was convicted for disturbing the peace by wearing a jacket that read "Fuck the Draft" in a state courthouse.

[14] Due in part to increasing domestic opposition, the United States reduced its involvement in Vietnam and completed withdrawal of its forces in 1973; the draft ended the same year.

On January 21, 1977, the day after his inauguration, President Jimmy Carter signed Executive Order 11967, which granted a full pardon to anyone who had committed or been convicted of a non-violent violation of the Selective Service Act.

The same provision in § 462(b)(3) of the act under which O'Brien was convicted remains law, though destroying draft cards is no longer a common form of protest and recent arrests for that offense are unknown.

[18] Finally, in 1972, the court relied in part on O'Brien to invalidate a law that prohibited picketing outside public schools that was not related to a labor dispute.

Quoting O'Brien, the court held that the law "imposes a selective restriction on expressive conduct far 'greater than is essential to the furtherance of [a substantial governmental] interest'".

[19] Two years later, the court declared in Spence v. Washington that the O'Brien test was "inapplicable" when the asserted government interest "directly related to expression in the context of activity".