The information was provided as the US Department of Justice conducted a secret probe into the editor and publisher of WikiLeaks, Julian Assange.
A statement from WikiLeaks said the Met had confirmed the sharing of information with Washington since at least 2013. The staff whose information was shared included former investigations editor Sarah Harrison, editor-in-chief Kristinn Hrafnsson and section editor Joseph Farrell.
The three journalists became aware in 2014 that an East Virginia court had ordered Google to provide their emails, contacts, log-in IP addresses and calendar entries to the US as part of an investigation into alleged violations of US Federal laws such as the Computer Fraud and Abuse Act and the US Espionage Act.
Manning, whose 35-year jail term, was commuted by former president Barack Obama, was arrested again last week when she refused to testify before a grand jury probe into WikiLeaks.
The role of the Met was exposed following a ruling by the information appeal tribunal in November which ordered the Met to confirm whether it was in possession of correspondence on the three WikiLeaks members.
The order was made in the wake of a legal challenge by Italian journalist Stefania Maurizi who works for La Repubblica.
Assange has been taking refuge in the Ecuadorian embassy in London since 2012. His problems began when he visited Sweden in August 2010 to attend a conference where he was scheduled to give a talk. During that visit, he had sex with two women whom he met. The pair filed rape and molestation complaints against him later, claims that he denied.
He was questioned by Swedish authorities and cleared. He could have left the country then and there, but stayed for a while, in case the authorities decided to question him again.
Interpol issued a Red Notice for his arrest on 20 November 2010. On 27 November, Assange surrendered to authorities and appeared before a Westminster judge. He was granted bail in December after his backers provided £240,000 in cash and sureties.
A legal back and forth eventuated and went on until June 2012, when Swedish prosecutors sought his extradition.
Assange's lawyers, among them the world-renowned Australian Geoffrey Robertson, replied that if he agreed to the extradition request, then he could be flown to the US from there.
On 19 June 2012, he jumped bail and took refuge in the Ecuadorian embassy, seeking asylum in the South American country. British police surrounded the building and blocked any chance of his leaving.
Ecuador granted him asylum in August 2012. He has had to stay inside the four walls of the embassy since then. He was granted Ecuadorian citizenship by a former president of the country, Rafael Correa.