Mohammed Kozbar, the chairman of Finsbury Park Mosque in north London, said members of Islington's differing faith communities had come together as part of the weekend's Great Get Together, a year on from the politician's murder.
One man died and 10 people were injured after a white van ploughed into people gathered outside the Muslim Welfare House in Seven Sisters Road early on Monday.
After a moment's silence, Mr Kozbar delivered a joint statement on behalf of faith groups, telling reporters the community event had taken place at the centre on Saturday.
"We met to remember Jo Cox, to honour and celebrate her affirmation that we all have more in common than we have things which differentiate us," he said.
"We met to celebrate our friendship and our co-operation for the good of our neighbourhood.
"Less than 48 hours later, the same area experienced a terrorist attack aimed at killing Muslims returning home after their Ramadan prayers."
Joined by Labour leader and local MP Jeremy Corbyn, he added: "An attack on one faith is an attack on all faiths and communities. Those who try to divide us and aim to spread fear, hatred and division will not succeed."