Christopher Rawding, 36, was employed by Nike to collect money from retail chains which placed significant orders.
But between 2015 and 2018 he siphoned off £890,000 collected from two retailers into his own bank account in order to satisfy his addiction.
Northumbria Police said Rawding’s actions were a “clear and prolonged abuse of trust”.
Det Con Alan Lowery added: “His greed has had a significant effect on the retailers who continued to pay him in good faith, in the belief that their funds were being passed on to Nike.”
Rawding spent up to £5,000 a day placing bets and tried to cover up the theft by using payments and credit balances from Nike’s other customers to clear the retailers’ account balance, the force said.
He pleaded guilty at a magistrates hearing in October 2019 to two counts of fraud by false representation .
Rawding, of Belsay Gardens, Sunderland, was sentenced on Tuesday at Newcastle Crown Court to 40 months in prison.
Proceedings have also been launched to recover any remaining money.