Richard Causey's deal with prosecutors could have a major impact on the case against his co-defendants, former chairman Kenneth Lay and former president Jeffrey Skilling.
The trial, originally scheduled to begin January 17, has been postponed until January 30 in order to allow defense lawyers to better prepare their case.
Causey had been charged with more than 30 criminal counts but reached a deal with prosecutors to plead guilty to just one count of securities fraud.
He will now serve no more than seven years in jail and if prosecutors are satisfied with his level of cooperation they said they would ask the judge to reduce that sentence to five years in jail.
Trouble for defence
"This is bad news any way you shake it for the defence," said David Berg, a Houston-based civil and white collar trial lawyer.
Lay and Skilling face fraud, conspiracy and other charges in relation to the alleged financial and accounting misdeeds at the company whose spectacular collapse into bankruptcy in 2001 rocked financial markets and undermined investor confidence corporate governance.
"It's a very good development for the government because it not only provides them with key insider testimony but provides them with the possibility of significantly shortening the trial," said Robert Mintz, a former federal prosecutor.
"They can begin one step closer to the top of the corporate structure and avoid the potential pitfall of losing their case in a series of mind numbing technicalities."
The fact that prosecutors were willing to offer such a generous deal just weeks before the trial was scheduled to begin indicates they may have been uneasy about the strength of their case, Mr Mintz said.
While the testimony of former chief financial officer Andrew Fastow, who pleaded guilty to conspiracy and securities fraud last year, will be crucial, Causey will serve as a better witness for the prosecution, Mr Mintz said.
"Fastow brings the negative baggage of having lined his own pockets with these off-book partnerships and has largely been credited with being the architect of these schemes to defraud investors," he said.
"Causey doesn't present the same bull’s eye for the defense."
Enron fall
Over 4,000 Enron employees lost their jobs when the giant energy company declared bankruptcy in 2001. Many employees also lost their life savings which had been invested in Enron stock.
The company's spectacular fall came after the US Securities and Exchange Commission began investigating Enron's accounting practices and found that it had used questionable and complex partnerships to hide almost one billion US dollars in debt and losses.
To date, 34 defendants have been charged, including 25 former Enron executives with 17 defendants convicted.
Causey began his career at now-defunct accounting firm Arthur Andersen where he spent nine years working primarily on the Enron account. He was hired by Enron in 1991 and did accounting work on Fastow's questionable side deals.
An affable and considerate man who was known as "the Pillsbury Doughboy", Causey was promoted to chief accounting and information officer at age 37.
He penned damning memos and painted a rosy picture of Enron's economic health during conference calls with analysts even while the company was disintegrating.
He has also been accused of using creative accounting to make it look as though the company was matching Skilling's earnings targets.