Dean Fisher, 36, used some of the cash to buy a Rolex and hire a Range Rover - and also splurged money at the bookies after becoming addicted to gambling.
The administration production manager spent £8,000 on a gastric bypass operation to shed weight from his 26 stone frame.
He got time off work to have a large section of his stomach removed in a private operation by telling colleagues at independent agency TCS Media he had cancer.
About £260,000 was poured into Croydon Athletic Football Club by Fisher and was used to keep the club afloat and bring in new squad members.
Fisher lost a total of £130,000 online in betting shops and at the races because of his gambling problem.
A further £140,000 was blown on luxury items for himself - including the operation and the lavish watch and car.
The fraud began in May 2008 when Fisher told his bosses he could save them money on printing paper by buying it from an alternative company. He forged a series of invoices for orders of paper and diverted the money to himself.
The scam unravelled in August the following year when bosses noticed no printing paper had been delivered to match the invoices. When confronted by his employers Fisher immediately confessed to his crime in a long email.
He pleaded guilty to one count of fraud at Southwark Crown Court on 4 June this year.
The court heard the father of four has since sold the family home in Caterham, Surrey, he jointly owned with his wife and has given £26,000 back to TCS where he had worked for fifteen years. His wife and children have been left with nothing and are now living in rented accommodation.
Prosecutor Usha Shergill said: "In addition to his employment he was also a director and chairman of Croydon Athletic Football Club and, to use his own words, that club was a very significant part of his life.
"Mr Fisher felt he had to take steps to keep the club in business otherwise there was a real danger it would fall.
"He embarked on an elaborate scheme to steal money from his employer to the total of £525,825 and use the money to pay for club bills and football players to the amount of £260,000.
"He didn't cope with the pressure and started to gamble very heavily. Unfortunately his gambling habit snowballed dangerously.
"Mr Fisher also admitted to having an operation done for a gastric bypass, which cost £8,000.
"The rest of the money was used by him to hire a Range Rover. When asked about the car he told colleagues his father had presented it to him. He also purchased a Rolex watch.
"Mr Fisher took days off work having told colleagues he was having treatment for cancer. He managed to convince colleagues this was the case and they were initially very supportive of him.
"However this was not the case. In actual fact he was at the races and on one occasion he was in hospital having stomach surgery carried out privately."
The court heard Fisher will eventually have to pay all the money back to TCS. The website of the company, based in Bayswater, West London, said: "TCS Media is one of the UK's leading independently owned media and advertising agencies."
In a victim impact statement managing director Simon Parker said: "After Dean confessed it left me cold. Not only was the business on its knees with the economic climate, but we now found out we had been defrauded for £500,000.
"We were also shocked and upset to discover Dean had never suffered from cancer but used £8,000 of the company money to have a private operation."
Jailing Fisher, who wept in the dock as he was sentenced, Judge John Price said: "You were in a position of trust and you breached that for all the wrong reasons.
"You were trying to support a club which you had no right to steal to support. You spent money on luxury items, the car, the Rolex, almost ruining the company.
"You tried to look big and were prepared to steal from the company to do it."
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