Jonathan Houseman shot dead business partners Will Henry, 31, and Brian McIntosh, 29, over hundreds of thousands of pounds he owed them.
The pair were executed after being lured to Albion Works, off Moor Street in Brierley Hill, last September.
Houseman, 33, from Stourbridge, was convicted of murder by a jury at Birmingham Crown Court.
Richard Avery, 33, had also been accused of helping to plan the killings but was found not guilty of murder. Avery was, however, convicted of perverting the course of justice.
His partner Francesca Scott was cleared of the same charge and walked free from court.
Houseman had claimed a mysterious fourth man in the Range Rover was responsible for the murders but that explanation did not wash with the jury.
Houseman was seen on CCTV getting in and out the car. No fourth man was ever seen.
The friends were shot a combined six times at close range.
The trial heard they had grown frustrated with Houseman for failing to pay them for work but were still willing to do business with him and were seemingly unaware they were targets.
The shooter was today described as "cold and calculated" by the lead detective who helped bring him to justice.
Mr McIntosh and Mr Henry were found dead in the Range Rover on September 30 last year but any suggestions this was some sort of gangland hit were quickly ruled out by police.
It transpired Houseman had murdered them in order to escape a mountain of debt he had got himself into. It's thought he could have owed as much as £400,000 to the victims.
Despite being cold enough to carry out the murders, CCTV and phone records would ultimately be the killer's downfall.
He was forced to admit it was him on camera at the yard with the victims when the murders happened. Detectives had him in a corner and he was always facing an uphill battle from there.
The jury were out deliberating for two days and returned a unanimous guilty verdict on Houseman.
There was a gasp from the public gallery as the verdict was delivered but the court otherwise remained quiet.
Houseman and Avery will both be sentenced at a later date.