Mark Connolly, 44, was found guilty by the jury this afternoon, Thursday, after more than two days of deliberation.
A unanimous verdict was returned on the four counts of manslaughter and three counts of breaching Health and Safety laws.
He will be sentenced tomorrow, Friday, morning.
Colin Buckley, 49, and Darren Burgess, 30, both of Carnforth; Chris Waters, 53, of Morecambe; and Garry Tindall, 46, of Tebay, were all killed when the runaway wagon laden with 16 tonnes of steel crashed into them at 40mph in the early hours of February 15, 2004.
The men were among a group of ten workers who were carrying out maintenance work on the West Coast mainline.
They were all employed by Connolly's company MAC Railway Services, who were acting as sub-contractors for Carillion Rail.
During the eight week trial, the court was told how Connolly was responsible for the deaths of the four workers by failing to carry out vital repairs to the wagon.
Jurors heard how the hydraulic brake system on the three tonne flatbed trailer was found to have been disconnected.
Investigators also discovered the hydraulic tubes had been filled with ball bearings, rather than brake fluid, to give the impression that everything was above board.
Instead, wooden chocks were being used to stop the trailer moving.
But the wagon laden with the steel railway track over-ran the wooden chocks, travelling almost four miles down the track before hitting the four workers.
Jurors also heard the men were unable to hear the approaching wagon because they were wearing helmets designed to protect against the noise of a generator.
The wagon travelled another four miles before coming to rest at a viaduct.
Connolly was accused in court of deliberately sabotaging the wagon for financial gain.
In the last year two memorials to the four men have been unveiled at Carnforth railway station and at the spot where they died in Tebay.
During the eight week trial the six men and six women of the jury were also taken to the site of the accident in south Cumbria to see for themselves the spot where the four men lost their lives.
They are still considering their verdict on Connolly's employee Roy Kennett, 29, of Maidstone, Kent, who denies four counts of manslaughter.