"Snowden's case has shown the need to protect persons disclosing information on matters that have implications for human rights, as well as the importance of ensuring respect for the right to privacy," Pillay said in a statement, referring to the rogue intelligence technician who last month revealed details of vast US surveillance programmes.
"National legal systems must ensure that there are adequate avenues for individuals disclosing violations of human rights to express their concern without fear of reprisals," she said.
People who blow the whistle from within intelligence agencies must also be protected, Pillay said.
Martin Scheinin, a UN expert on fundamental freedoms, agreed, pointing out in the statement that "reliable factual information about serious human rights violations by an intelligence agency is most likely to come from within the agency itself."
"In these cases, the public interest in disclosure outweighs the public interest in non-disclosure," he said, insisting "such whistleblowers should firstly be protected from legal reprisals and disciplinary action when disclosing unauthorised information."
Pillay also implicitly criticised the rapid rejection of most of Snowden's asylum applications, which he has sent to more than 20 countries in a bid to avoid US authorities after being charged with espionage.
"Without prejudging the validity of any asylum claim by Snowden, I appeal to all states to respect the internationally guaranteed right to seek asylum . . . and to make any such determination in accordance with their international legal obligations," she said.
Since shortly after sparking one of the biggest intelligence leaks in US history, Snowden has been marooned at a Moscow airport without official travel documents.
He said he wanted to claim asylum in Russia until he can travel on to Latin America, where Venezuela, Bolivia and Nicaragua have all indicated they would be willing to offer him a safe haven.