Stirling Supply Limited, based in Holbrook Lane, Coventry, rented out the three-storey house in Oliver Street.
Rugby Borough Council's housing enforcement team secured a warrant to inspect the property after receiving a tip-off from a member of the public.
The inspection took place in June 2016 and officers established seven tenants were living at the house - which had sufficient beds and mattresses to sleep up to 11 tenants.
HMO regulations stipulate a property comprising three storeys and shared by five or more tenants in separate households must be licensed by the council.
The inspection also discovered the house had no fire or smoke detectors.
An investigation confirmed Drahomir Cureja, of The Severn, Daventry, had day-to-day responsibility for managing the property.
When interviewed under caution, Mr Cureja admitted there were five tenants living at the property.
But giving evidence at Nuneaton Justice Centre during a hearing on Thursday 15 June, Cureja said only four tenants were housed at the property - and claimed he was only the handyman, despite evidence showing he had signed the tenancy agreement for the house on behalf of Stirling Supply Limited, collected the rent from tenants and paid it to the owner of the property.
Cureja pleaded not guilty to managing an HMO without a licence and failing to provide fire detection equipment at the property.
But after being found guilty by magistrates, the 36-year-old was fined a total of £1,000. He was also ordered to pay £500 costs and a £100 victim surcharge.
Stirling Supply Limited faced a charge of failing to provide fire detection equipment at the HMO.
A representative of Stirling Supply failed to attend court and the company was found guilty in its absence.
It was fined £8,000 and ordered to pay £2,459 costs and a £170 victim surcharge.
Speaking after the hearing, Cllr Lisa Parker, Rugby Borough Council portfolio holder for environment and public realm, said: "The HMO regulations place a responsibility on landlords to ensure tenants live in clean and safe accommodation.
"Our housing enforcement team works with landlords to explain the regulations and make sure all HMOs in the borough comply with legislation.
"However, when landlords break the law we have no hesitation in taking the case to court, as our number one priority has to be the health and wellbeing of tenants."
Tenants with concerns about conditions at a rented property can report the matter to the council's housing enforcement team anonymously by completing the online form at www.rugby.gov.uk/housingenforcement
Landlords who need advice on HMO regulations can contact the team on (01788) 533882 or email ept@rugby.gov.uk