Feriz Mehmood, 50, of Coronation Drive, Elm Park, admitted 16 offences relating to a house in multiple occupation (HMO) In Thorn Lane, Rainham, where he housed 10 people, including four children.
Havering Council said the breaches “put the lives of his tenants at risk”.
Council leader Ray Morgon said: “All our residents deserve to live in safe accommodation.
“We will continue to crack down on irresponsible landlords taking advantage of families and individuals by providing poorly maintained HMO properties.
“We won’t tolerate it and neither will we stand for landlords not having the correct licences.”
Mehmood failed to provide gas and electrical safety certificates when requested and neglected critical fire safety measures, the council said.
These included ensuring working smoke detectors and installing appropriate fire doors.
The property was also infested with cockroaches, which the council said he failed to address, and lacked adequate kitchen facilities for the number of occupants.
At Barkingside Magistrates Court on June 3, Mehmood pleaded guilty and was fined £12,000, ordered to pay £2,227.89 in costs, and given a £2,000 victim surcharge, bringing the total to £16,027.89, payable by July 1.
Cllr Morgon said the council is committed to supporting responsible landlords but will not hesitate to take tough action against those who break the law.
He said: “We are also here to support landlords and work alongside them to help them make sure tenants are living safely in private rented accommodation in Havering.
“However, landlords of HMOs that break the rules like in this case must be aware we will use the strongest possible action against them.”
