The notoriously outspoken Livingstone seldom apologises for anything, but he choked up as he read an account of the brutal tortures suffered by slaves in Britain's Caribbean colonies.
And the politician once nicknamed 'Red Ken' for his left-leaning views angrily denounced the role of his city's corporations in financing the trade.
"You can look across there to see the institutions that still have the benefit of the wealth they created out of slavery," Livingstone said, pointing through a huge window at the skyscrapers cluttering London's financial district.
"As mayor, I offer an apology on behalf of London and its institutions for their role in the transatlantic slave trade."
US civil rights campaigner the Reverend Jesse Jackson praised the statement, saying Livingstone broke important ground with his remarks.
Last Mod: 24 Ağustos 2007, 10:26
Jackson said apologies should lead to reparations.
Livingstone did not explicitly mention restitution, but his tearful expression of remorse went further than then-Prime Minister Tony Blair's statement on the 200th anniversary of the law that ended the slave trade in March.
Blair expressed his deep sorrow, but did not make a direct apology.
Livingstone said London would mark the horrors of slavery with an annual memorial day timed to coincide with the UN's International Day for the Remembrance of the Slave Trade and its Abolition, held every August 23.
London played a central role in the slave trade, outfitting, financing and insuring many of the ships that ferried living cargo to plantations in the New World. Revenue from the trade helped fund the construction of London's docks.
London is not the first to apologise for the trade. Liverpool, one of the great European slave-trading ports, formally apologised in 1999.