Graham Houghton, 33, embezzled cheques from Brewin Dolphin Security, an international stocks and shares company where he worked as a manager.
Newcastle Crown Court heard how over seven years Houghton got 129 cheques authorised by claiming to his bosses they were going to clients.
But Houghton, who had an addiction to on-line gambling, horse racing and casinos, had run up almost half-a-million pounds-worth of debt and was using the stolen cash to cover it.
Prosecutor Kingsley Hyland told the court: "This was a systematic breach of trust on a significant scale over a seven year period. The defendant was in a significant position of trust and it was clear procedures of checking the legitimacy of each cheque request was not followed."
Houghton, of James Street, Sunderland, was collared after he was made redundant from the Newcastle company in 2004 and a discrepency with one cheque sparked a more thorough investigation.
He admitted 28 charges of obtaining money transfers by deception between December 1997 and June 2004 and asked for further similar charges to be taken into account.
Defence barrister Richard Bloomfield told the court how Houghton's gambling affliction has been diagnosed as a mental illness by his GP.
Mr Bloomfield said: "He did not misappropriate the money with the intention of forever keeping it, but it was a spiral he got into which he could not get out of. "