Martin Gutaj, 44, of Brentford, and his company Martinisation London Limited were found guilty at the Old Bailey.
Gutaj was found guilty of two safety charges while Martinisation London Limited was found guilty of two counts of corporate manslaughter.
Gutaj was bailed to appear at the Old Bailey on Friday July 7 for sentencing.
The court heard how on 21 November 2014, Tomasz Procko, 22 and Kyrol Szymanski, 29, both Polish nationals went to work and never returned home.
The men were working at a construction site in Cadogan Square run by Gutaj’s company.
During the course of the day the men were asked to perform a lifting operation at height without supervision and the requisite training.
The victims were not provided with a plan, method statement or risk assessment prior to the task being undertaken, thereby exposing them to the risk of serious harm.
The expectation was for the workmen to use a rope to haul a sofa over a balustrade and into a first floor apartment.
Advice from an experienced and reputable lifting company on how to carry out the process safely was ignored due to time and budgetary constraints.
Both workmen fell after railings on the balcony gave way whilst the furniture was being manoeuvred into premises.
Police were called and officers, paramedics and London’s Air Ambulance attended.
Tomasz Procko was pronounced dead at the scene.
Karol Szymanski was taken to a central London hospital in a critical condition where he later died.
Detective Sergeant Simon Rogers from the Homicide and Major Crime Command said: “Tomasz Procko and Kyrol Szymanski fell to their deaths during the lifting operation which was entirely foreseeable and avoidable.
Martinisation London Limited and the operation director Martin Gutaj failed in their duty of care to protect the men.
“This was a complex investigation led by the Metropolitan Police Service who worked closely with Heath and Safety Executives over a 30 month period.
“We hope that the verdicts today offer some comfort to the bereaved families who have continued to support the investigation throughout.”