WASHINGTON  — On Wednesday, the U.S. Supreme Court ruled that police officers usually need a warrant before they can search an arrested suspect’s cell phone, a major decision in favor of privacy rights at a time of increasing concern over government encroachment in digital communications.

In an opinion written by Chief Justice John Roberts, the court said that the right of police to search an arrested suspect at the scene without a warrant does not extend in most circumstances to data held on a cell phone. There are some emergency situations in which a warrantless search would be permitted, the court noted.

The unanimous 9-0 ruling goes against law enforcement agencies, including the U.S. Department of Justice, which wanted more latitude to search without having to obtain a warrant. The ruling is a win for digital privacy advocates.

“We cannot deny that our decision today will have an impact on the ability of law enforcement to combat crime,” Roberts wrote.

The court was weighing two separate cases that pitted evolving expectations of privacy against the interests of the law enforcement community as the court for the first time weighed the increasingly ubiquitous role of cell phones in modern day life.

The ruling appears to be in line with public opinion based on results of a Reuters/Ipsos opinion poll, which found that 60.7 percent of people surveyed said police should not be allowed to search cell phones without a warrant.

Cell phones, initially used purely to make calls, now contain a wealth of personal information about the owner, including photographs, video and social media content. According to a 2013 report by the Pew Research Center, 91 percent of adult Americans have a cell phone, more than a half of them smartphones that can connect to the Internet.

Concerns about increasing government encroachment on personal privacy, especially in relation to electronic communications, has surged into the public eye over the last year after disclosures made by former National Security Agency contractor Edward Snowden about government surveillance.