The Women's March on London event, which 40,000 people had pledged to attend, is being held in conjunction with others taking place in cities across the world to promote women's and human rights.
Several thousand people across all ages and genders descended on Grosvenor Square in London on Saturday before the rally at 2pm.
They came holding a rainbow of placards with slogans such as 'dump Trump', 'reject hate, reclaim politics' and 'no to racism, no to Trump'.
Beginning at the American Embassy in London, the march on Saturday will snake its way around the streets of the capital and finish with a rally in Trafalgar Square.
Marches are also happening in other UK cities including Manchester, Edinburgh, Belfast, Liverpool and Cardiff, with thousands expected to attend.