The inaugural resolution sponsored by the U.S. since it joined the council in June broke a long-running deadlock between Western and Islamic countries in the wake of the publication of cartoons depicting the Muslim Prophet Muhammad.
The resolution has no effect in law but provides Muslim countries with moral ammunition the next time they feel central tenets of Islam are being ridiculed by Western politicians or media through "negative racial and religious stereotyping."
American diplomats say the measure _ co-sponsored by Egypt _ is part of the Obama administration's effort to reach out to Muslim countries.
"The exercise of the right to freedom of opinion and expression is one of the essential foundations of a democratic society," the resolution states, urging countries to protect free speech by lifting legal restrictions, ensuring the safety of journalists, promoting literacy and preventing media concentration.
Rights groups cautiously welcomed the resolution as an improvement on earlier drafts, but said Egypt was in no position to lecture other countries about free speech as it has a poor record on the matter.
"Egypt's cosponsorship of the resolution on freedom of expression is not the result of a real commitment to upholding freedom of expression," said Jeremie Smith, Geneva director of the Cairo Institute for Human Rights Studies.
"If this were the case, freedom of expression would not be systematically violated on a daily basis in Egypt," he said.
Others warned that the resolution appears to protect religions rather than believers and encourages journalists to abide by ill-defined codes of conduct.
"Unfortunately, the text talks about negative racial and religious stereotyping, something which most free expression and human rights organizations will oppose," said Agnes Callamard, executive director of London-based group Article 19.
"The equality of all ideas and convictions before the law and the right to debate them freely is the keystone of democracy," she said.
Although the resolution was passed unanimously, European and developing countries made it clear that they remain at odds on the issue of protecting religions from criticism.
Some Asian and African countries had called for stronger condemnation of articles, cartoons and videos they believe defames Islam.