Amanda Rees, of Olive Mount, St Helens, joined the manufacturing firm based at Runcorn’s Astmoor Industrial Estate in 2010.
Three years later she began siphoning money belonging to the company into her personal bank accounts.
The 34-year-old continued to do so until last November, the point at which the firm realised what Rees had been doing.
The company reported Rees to the police and a subsequent investigation revealed that she had stolen a total of £980,673 from the firm.
The mum-of-three admitted being responsible for the thefts spanning six years when she voluntarily attended a police station and was interviewed by the investigators on Saturday 14 March.
Rees was subsequently charged with seven counts of theft and one count of money laundering.
She pleaded guilty to the charges and was sentenced at Chester Crown Court on Tuesday 3 November.
Sergeant Phil Brown, who led the investigation of behalf of Runcorn Local Policing Unit, said: “Employed as an admin manager, Amanda Rees was responsible for the company’s outgoings and had full access to its bank accounts.
“The firm placed a high degree of trust in her for this role, but unfortunately that trust was misplaced.
“Over several years Rees transferred large quantities of money from the company’s bank account into her own accounts.
“The stolen money, which totalled nearly £1 million, funded a lavish lifestyle for Rees and her family.
“Once her offending came to light Rees admitted being responsible for the thefts and money laundering at the first opportunity to do so.
“When questioned by officers she claimed that she was suffering from depression and had stolen the money as a way of self-medicating, with buying luxury items for herself and her family making Rees feel better.
“She admitted paying for her wedding, cars, home improvements and holidays with the money she stole, as well as luxury items such as hot tubs.
“Rees also admitted volunteering to work from home when on maternity leave so that no-one else would have to deal with the company’s finances and her offending would not be uncovered.
“She is now behind bars facing the consequences of her actions and I hope that this case deters others from committing similar offences.”
David Keane, police and crime commissioner for Cheshire, added: “I would like to thank all the officers that have been involved in the investigation for their endeavours to secure this conviction.
“I hope that the conviction and the custodial sentence imposed by Chester Crown Court provides the company that is the victim in this case with some closure.”