Detective Chief Inspector April Casburn was charged with misconduct for phoning the News of the World tabloid and offering to pass on information about whether London's police force would reopen its stalled phone-hacking investigation.
Prosecutors said the tabloid did not print a story based on her call and no money changed hands but she had committed a "gross breach" of the public trust by offering to sell the information.
Casburn, 53, also was accused of trying to ruin the phone-hacking inquiry — which centred on Murdoch journalists at the now-defunct News of the World — by leaking information to the press.
A key witness testified that Casburn wanted to torpedo the hacking inquiry because she feared it would drain resources from the fight against terrorism. The witness said she also was upset about the purported pressure being put on prosecutors by John Prescott, a deputy prime minister under Tony Blair who had been a hacking victim.
Prosecution lawyer Greg McGill said Casburn was guilty of a "very serious offence."
The Metropolitan Police said in a statement that selling confidential information to journalists for personal gain would not be tolerated and that Casburn had "abused" her police position.
"Casburn proactively approached the News of the World, the very newspaper being investigated, to make money," the police statement said. "She betrayed the service and let down her colleagues."
The statement said vital information on the Casburn case was given to police by the Management and Standards Committee at Murdoch's News Corp.
Casburn, who managed the Metropolitan Police terrorist financing investigation unit, had admitted contacting the newspaper but denied that she offered confidential information or had sought payment.
Jurors at Southwark Crown Court found her guilty of one count of misconduct. She will be sentenced later this month.
Britain's long-running phone-hacking scandal has led to dozens of arrests and to criminal charges against prominent journalists, including Prime Minister David Cameron's former communications chief. Other police officers and civil servants have also been questioned about possible wrongdoing.
The phone hacking scandal has involved allegations of illegal snooping on celebrities, crime victims, politicians and others. Media mogul Murdoch closed the News of the World tabloid in July 2011 after many of its misdeeds were exposed. His media company has also paid out millions to numerous victims to avoid lengthy and expensive trials.
Tim Wood, the News of the World news editor who took Casburn's call, told the court that the detective expressed concern that counterterrorism resources were being diverted to the phone-hacking investigation. Wood also said Casburn complained of interference from Prescott, a prominent hacking victim and a vocal Murdoch critic.
"The one thing that stands out in my mind is the fact that she kept going on about Lord Prescott," Wood said. "Her saying that he was pressing for them to put charges on the News of the World, and she was saying that she felt it was wrong that he was interfering in the scandal, so to speak, and she resented that."
Casburn has been suspended with pay, the force said.
A News of the World reporter and a private investigator were jailed in 2007 for hacking into the voicemails of royal aides. But the newspaper denied there was a wider problem and the police investigation was closed.
Police reopened the investigation in early 2011 as new evidence emerged about the scale of the law-breaking.