Richard Causey, former top accountant of fallen US energy giant Enron, has pleaded guilty to securities fraud before a US judge.
Causey once handled the accounts of the seventh-largest US firm
Mr Causey was attending a court hearing ahead of the trial next month of Enron's two top executives.
The ex-accountant said he would plead guilty in exchange for a possible seven-year jail sentence.
As part of the plea bargain it now looks likely that Mr Causey will testify against his former bosses.
Richard Causey was due to go to trial on 17 January with Enron's former chairman Kenneth Lay and former president Jeff Skilling.
However, in light of the latest development, the trial has now been delayed until 30 January.
Enron collapsed three years ago with massive debts, provoking a national scandal in the US.
Mr Causey was a key figure in the scandal amid revelations the company had hidden billions of dollars in losses and had inflated its profits.
US prosecutors have accused Mr Causey and others of using "sophisticated tricks" to deceive the public about the company.
Shortly after Mr Causey's arrest last year, one of his lawyers said his client had done "absolutely nothing wrong".
By agreeing to testify against his former bosses, Mr Causey should receive a much lesser prison sentence than he would if convicted on all counts.
He will serve seven years in prison and forfeit $1.25m (£0.72m) to the US government, according to the plea bargaining deal.
However, if federal prosecutors are happy with his cooperation, they can request that his sentence be reduced to five years.