All London boroughs have signed up to a rogue landlord checker which aims to "name and shame" the capital's unscrupulous agents.
The checker, set up by the Mayor of London, Sadiq Khan, allows local authorities to submit records of prosecutions and fines against dishonest landlords.
Renters can check if their prospective landlord or agent has any convictions.
Mr Khan said unscrupulous landlords and agents "have nowhere to hide".
"I'm confident this will be a major step in tackling unscrupulous and illegal practices in the rented sector," he said.
Among the records is a case involving a residential landlord which was fined £150,000 after being prosecuted by London Fire Brigade in May 2017, following a major fire at a block of flats it owned in Westminster in 2011.
Up to 13 people had to be evacuated and the subsequent investigation found a string of fire safety breaches, the Mayor said.
The database, published on the City Hall website, will give Londoners "greater confidence in renting a home, as well as acting as a clear deterrent to the small minority of landlords and letting agents who behave dishonestly", Mr Khan said.
London Fire Brigade's assistant commissioner for fire safety, Dan Daly, said: "Now that all boroughs have signed up, it means every Londoner who rents, wherever they live, will be able to find landlords and letting agents who have been successfully prosecuted or faced civil enforcement for housing offences, including those prosecuted by us for fire safety breaches."
It comes as the Mayor also published his London Housing Strategy, which outlines his approach to tackling London's housing crisis.
The strategy will be considered by the London Assembly at its next meeting.