Demonstrators assembled hours after a ceasefire was agreed in the wake of 11 days of conflict between Israel and Hamas in the Gaza Strip.
They congregated at Victoria Embankment before travelling towards Hyde Park.
Protestors holding banners, placards and flags let off green and red coloured smoke as they cried chants including ‘We are all Palestinians’ during the march.
Many wore costumes, masks and face paint while others draped themselves in the Palestinian flag.
Some clambered onto bus stops and lamp posts while others wrote ‘Free Palestine’ on the walls.
The group called out ‘Boris Johnson, shame on you’ when they reached Downing Street.
Among the organisations involved in the demonstrations are branches of the Palestine Solidarity Campaign, Stop The War Coalition and National Education Union.
A temporary stage was set up in Hyde Park for speeches to be made this afternoon.
Labour’s former Shadow Chancellor, John McDonnell, told crowds: ‘Yes, a ceasefire has been negotiated and we welcome a ceasefire.
‘But let’s be clear, there will be no ceasefire in our campaign to boycott, disinvest and sanction the Israeli apartheid state.
‘The message is clear; we will not cease our campaign in solidarity until there is justice. So let’s make it clear, no justice, no peace.’
Crowds responded by cheering and releasing fireworks and coloured smoke.
Protester Muktha Ali, 32, from Harrow, northwest London, said: ‘I’m here because this is now urgent, the Israeli occupation needs to end now, it’s been long enough.
‘Mothers, fathers, brothers, sisters and children have been bombed and murdered, Palestine has to be free.’
Another, named Jake, said: ‘I stand in solidarity with Palestinians, and so should everyone, no matter your nationality.
‘It’s great to see so many people come out in their thousands to support the cause. We will win – our cause will be heard.’
The protest is said to have been largely peaceful although a few people were seen throwing objects at police attempting to split crowds in Hyde Park.
The truce, which was agreed on Thursday evening and came into effect at 2am on Friday morning, ended the fourth Israel-Hamas war in just over a decade.
The ceasefire was praised by both the Prime Minister and Foreign Secretary, Dominic Raab.
But it was less than a day before violence erupted after Israeli police stormed the Al-Asqa Mosque shortly after prayers on Friday.
At least 232 Palestinians, including 65 children, were killed during the 11 days of violence, Gaza’s Health Ministry said.
Israeli authorities said at least 150 of those killed were militants.
Some 12 people including two children have perished in Israel, according to the country’s medical service.
Celebrities including Idris Elba, Rihanna and model Bella Hadid – whose father is Palestinian – joined growing calls for the bloodshed to end.