Writing for the Court, Chief Justice Earl Warren held that the law prohibiting the willful destruction of draft cards did not violate the right to free speech because it was content-neutral and narrowly targeted to achieve a substantial government interest. Although O’Brien argued that the law was passed only to stifle the free speech of anti-war protestors, Warren reasoned that Congress’ supposed intention did not matter so long as the law could be justified on another basis, stating that “this Court will not strike down an otherwise constitutional statute on the basis of an alleged illicit legislative motive.”

Warren found that in determining the constitutionality of a statute that prohibits conduct including elements of speech and non-speech, the government must have a substantially important interest in regulating the non-speech element to justify the abridgment of the freedom of speech. To measure this, Warren found that a law is “sufficiently justified” if it meets the following criteria:

• The law is within the constitutional power of the government

• The law furthers an important or substantial government interest

• The government’s interest is unrelated to the suppression of free expression

• The law restricts no more speech than necessary to achieve the government's interest.

Warren concluded that the law prohibiting the willful destruction of draft cards met each of these criteria and was thus constitutional.