Sadiq Khan held the meeting in Lambeth after visiting a farm project run by the Oasis Trust.
Oasis City Farm was derelict wasteland until the church transformed it into a farm that does community projects, outreach with young people, community meals and a food bank.
The MP met with some of the young people working on the site before his discussion with London's Christian leaders.
He told Premier: "It's been inspirational seeing the work taking place here at Oasis Farm.
"The local church, the Oasis Church, is actually being a community hub, getting young people and volunteers involved.
"They're working with businesses to improve this piece of land, it was a derelict horrible piece of land."
He added: "There's a word that's used called outreach - people of faith not simply staying in their congregation or prayers but actually going into the community to do social action.
"Just look at the foodbanks Oasis provides, think about the schools their involved in and the community work they do."
Sadiq Khan speaking to Premier's Antony Bushfield: