Campaigners chanting Jeremy Corbyn's name marched through central London against austerity and the Conservatives.
A number wore t-shirts with Corbyn and a tick printed on them and one banner featured the Labour leader riding on a unicorn under a rainbow.
The crowd repeatedly took up the chant of "oh Jeremy Corbyn" and "Tories out" during the rally on Saturday afternoon.
Many carried banners saying Tories Out, with one reading No DUP, No sanctions, No more while another said Capitalism Kills. Organise To Fight Back. Justice For Grenfell. Safety For All.
The protest assembled at BBC Broadcasting House in Portland Place before moving on to Parliament Square.
There was a strong police presence at the demonstration, with some of the roads around the square closed to traffic.
Shadow chancellor John McDonnell vowed to support the victims of the Grenfell Tower fire in west London when he spoke at the event.
He said: "To the victims of Grenfell Tower we pledge now, we will stand with you and your families all the way through.
"We bring you sympathy but more importantly we bring you solidarity.
"We will not rest until every one of those families is properly housed within the community in which they want to live.
"Grenfell Tower symbolised for many everything that's gone wrong in this country since austerity was imposed upon us."
He slammed the Tories for praising the emergency services "every time there's a tragedy" but then cutting jobs and wages.