Jessica Harper, 50, had been accused of submitting false invoices to claim payments between 2007 and 2011.
At the time she was working as head of fraud and security for digital banking and made false claims totalling £2,463,750. The prosecution said that she had carried out a "very simple fraud" and that she has "been convicted of the type of crime the bank employed her to combat".
It is thought that Harper laundered part of the proceeds buying property for her family, as well as spending some of the cash on improvements to a property in the south of France.
At Southwark Crown Court, Harper admitted a single charge of fraud by abuse of position by submitting false invoices to claim payments.
She also admitted a single charge of transferring criminal property – the money –that she had defrauded from her employers.
Harper was arrested on 21 December last year, before being charged in May.
She has already repaid £300,000 and is in the process of selling her house for about £700,000.
Questions are likely to be asked about why the bank's internal controls were not sufficient to detect the ongoing fraud, and why protocols could be undermined for such a sustained period.
Lloyds is now 39.7 per cent state-owned after being bailed out by the government during the financial crisis. The group has yet to comment on the case.
Harper, of South Croydon, south London, will be sentenced on 21 September.