Fifty-year-old Jessica Harper, from Croydon, pleaded guilty to fraud and money laundering at Southwark Crown Court.
Harper had been employed at Lloyds since 2000 and began submitting false invoices in December 2007.
The court heard that over the next four years she fraudulently took a total of £2.46m from her employers.
Harper began to defraud Lloyds just months before the taxpayer was forced to stump up £20bn for a rescue package for the troubled bank.
An internal investigation at Lloyds revealed her crime, but the timing was embarrassing for a bank which remains partially publicly-owned.
Antony Swift, prosecuting, described Harper's crime as "a very simple fraud" and said she had already repaid £300,000 and was in the process of selling her house for around £700,000.
"That will be some £1m out of £2.5m that's gone missing," he said.
Judge Nicholas Loraine-Smith allowed Harper bail, with strict conditions, until sentencing on September 21.
He said: "The Crown tell me she has co-operated and is unlikely to flee. In those circumstances I can grant her bail on condition of residence at her present home address.
"And there will be a curfew of 9pm to seven in the morning," he added.
Harper has already had to hand in her passport and was also ordered not to apply for any international travel documents.
Crown Prosecution Service Central Fraud Division head Sue Patten said: "Jessica Harper has today been convicted of the type of crime the bank employed her to combat.
"The evidence in the case was clear and left Harper with little choice but to plead guilty - In doing so, she has admitted to a huge breach of trust against her former employer.
"Harper was expected to safeguard the financial interests of the bank. Instead, she submitted false invoices totalling more that £2.4m over a period of four years.
Lloyds said in a statement: "As the court process is ongoing it would be inappropriate for us to comment."