Mourners held a minute's silence at 9.30am (0830GMT) to remember father-of-six Makram Ali, who died when Darren Osborne ploughed a hire van onto a crowded pavement close to Finsbury Park mosque, intending to kill as many Muslims as possible.
The attack, on June 19 last year, also left 12 injured.
Home Secretary Sajid Javid, London Mayor Sadiq Khan and opposition Labour leader Jeremy Corbyn Mohammed Mahmoud, all attended the event at nearby Islington Town Hall, along with the imam of the mosque, Mohammed Mahmoud.
"A man ridden with racism drove a vehicle into a crowd of people and tried to divide and destroy our community," said Corbyn.
"We will never allow them to destroy us. Stay united, stay together, support each other!", he added.
The mayor paid tribute to the response of the local community.
"The way this community has responded has inspired us all," he said.
"When Londoners face adversity we stand up for our values. This is our city, this is our way of life. For those who seek to divide us, the message is 'you will never succeed'."
Osborne, from the Welsh capital Cardiff, was in February sentenced to life in prison with a minimum 43-year term.
"Last year's cowardly attack which targeted innocent worshippers leaving Finsbury Park mosque is an attack on all of us," May said in a statement.
"As with all acts of terrorism the intention was to divide us but we will not let this happen.
