Christian, Muslim and Jewish leaders addressed a crowd of about 100 people who joined an interfaith vigil outside City Hall on Sunday evening to show solidarity with the people of Paris.
The event was organised by Citizens UK, the coalition of faith groups and community groups best known for its living wage campaign.
Introducing the vigil, Citizens UK trustee Dr Kaneez Shaid said: "As a British Muslim living in London, it breaks my heart to see terror being inflicted on innocent lives all over the world.
"No faith calls for the murder of innocent people. Not in our name!"
Methodist minister Revd Paul Regan said: "Nous sommes Paris! We stand united with the people of Paris at this time."
Dr Muhammad Abdul Bari of the Muslim Council of Britain described ISIS as a "monster cult".
He said: "Tonight's vigil is all about mourning and our solemn reflection and prayer for peace. It is to show our solidarity with victims in Paris and to strengthen our commitment to work together."
Dr Bari added: "This mass murder of innocent people in Paris must not be allowed to terrorise and divide us.
"Terrorists want to create hatred amongst communities by shouting religious slogans or nationalist rants.
"We reject their abominable hypocrisy."
Rabbi Danny Rich, chief executive of Liberal Judaism, said: "We commend the efforts of all in public service who tend the wounded, comfort the bereaved, protect the vulnerable and work to pursue the perpetrators.
"We call upon Jews, Christians, Muslims, Hindus – and those of all faiths and none – to endorse the values of pluralism and democracy which require respect for the rule of law and the rejection of terror."