Sadiq Khan, the new Labour Mayor of London, chose Southwark Cathedral as the setting for a ceremony where he signed the formal declaration of acceptance of office.
The ceremony took place less than 12 hours after the final declaration of the results of the mayoral election which came at 12.20am on Saturday morning.
The new Mayor signed the formal declaration watched by an array of faith leaders from around London, including the Bishops of Southwark and Woolwich and members of Southwark Cathedral's clergy.
Guests at the ceremony were welcomed by the Dean of Southwark, the Very Revd Andrew Nunn, who said he had been "delighted" to receive a call asking whether the cathedral would host this event.
Baroness Lawrence of Clarendon, introducing Mr Khan, said that Londoners had "chosen unity over division and hope over fear" by electing the Labour candidate.
Mr Khan said: "We are here in Southwark Cathedral because I want to start this mayoralty as I intend to go on.
"I am determined to lead the most transparent, engaged and accessible administration that London has ever seen – and to represent every single community and every single part of our city – as Mayor for all Londoners.
"So I wanted to do this signing-in ceremony here, in the heart of London, surrounded by Londoners of all backgrounds."
St Bonaventure's school choir from East London took part in the ceremony.