Andrew Skelton, 43, leaked details of nearly 100,000 supermarket staff after he was accused of dealing legal highs at work, prosecutors said.
He then tried to cover his tracks by using a colleague's details to set up a fake email account.
Skelton, of Water Street, Liverpool, denied three charges of fraud but was found guilty at Bradford Crown Court.
At his trial the jury heard how he abused his position as a senior internal auditor at the firm's Bradford head office.
He sent information about staff salaries, bank details and National Insurance numbers to several newspapers and posted it on data sharing websites, in a data breach which cost the company more than Â£2m to rectify.
David Holderness, from the Crown Prosecution Service, said: "Andrew Skelton's motive appears to have been a personal grievance over a previous incident where he was accused of dealing in legal highs at work.
"The potential loss to his victims and the sheer quantity of potentially compromised data was very significant and could have resulted in employees' identities being stolen.
"The sentence imposed today sends out a very clear message that we will robustly prosecute serious fraudsters such as Skelton who believe they are above the law."

The "unique window" has been installed in the church at the Royal Citadel to mark the 300th anniversary of the Royal Artillery.
A Merlin helicopter, soldiers and amphibious vehicles all feature in the scene.
The windows have been installed at The Royal Chapel of St Katherine Upon The Hoe within the Royal Citadel.
Karl Freeman MBE, the Vicar for 29 Commando Regiment, said: "It is quite unusual to see helicopters in church glass. Basically, there's an integration of faith into regimental life, which is my job."
Lieutenant Colonel Jon Cresswell, who is Commanding Officer of the regiment, said "We wanted to leave our mark here, and I think we've very much done that."

Middlesbrough Council has secured a £3.7m grant from the Heritage Lottery Fund (HLF) to restore the Town Hall in Corporation Road.
The council is putting £4m into the scheme which will turn the premises into a visitor "heritage" attraction.
Ivor Crowther, head of HLF North East, said it was a "stunning reminder" of the town's proud industrial heritage.
Parts of the Grade II listed building will be opened to the public, including the Victorian courtroom, cells and fire station.
The plans also include the development of a new cafe, bar, and a new community space.
Work is expected to get under way in January and the Town Hall is scheduled to be closed for nearly two years, the council said.
Middlesbrough's deputy mayor Dave Budd said: "The Town Hall is the jewel in Middlesbrough's crown and this project will restore it to its full majestic glory."
A Morrisons employee who posted staff data on the internet over a grudge has been jailed for eight years.
[NEXT_CONCEPT]
A military scene has been included as part of a stained glass window at a church in Plymouth.
[NEXT_CONCEPT]
Plans for a £7.7m revamp of a 120-year-old council building have been given the go ahead.