Kenneth Lay and Jeffrey Skilling now face long prison terms for the 2001 collapse which involved questionable accounting and arcane financing vehicles to hide an estimated $US40 billion ($A53.18 billion) in debt.
Thousands of people lost their jobs and life savings when Enron collapsed and the scandal undermined faith in corporate America and led to a massive stock market selloff.
Skilling, 52, was found guilty of 19 of 28 counts of fraud and conspiracy and faces a maximum penalty of 185 years in jail.
Enron founder Lay, 64, was found guilty of all six fraud and conspiracy charges he faced and federal bank fraud charges in a separate trial. He faces a maximum of 165 years in jail.
They will be sentenced on September 11. Both men had pleaded not guilty.
Skilling’s defence lawyer said that a vigorous appeal would be mounted. "I would like to thank my family for sticking by me," Skilling told reporters. "We fought a good fight and we didn't get the verdict we wanted."
It took less than six days for the eight women and four men of the jury to reach a verdict in the trial which started January 26.
"There must have been mounds and mounds of evidence because the jury came back very quickly," Houston securities lawyer Tom Ajamie said.
"This indicates the evidence was overwhelming. The jurors probably walked back into the jury room and said 'why were we sitting here for three months'? These guys are guilty."
The case, one of the most complex corporate crime cases in US legal history, represents the most high-profile test for the US government's crackdown on corporate wrongdoing.
The conviction was a vindication of the government's Enron task force, set up after one of the worst financial scandals in recent history which hurt confidence in corporate America.
Enron's collapse was precipitated by revelations that the company had hidden debts estimated at around $US40 billion ($A53.18 billion).
"From a deterrent standpoint, these two defendants were at the epicenter of the corporate governance scandal, and these convictions would remind people of the rather severe consequences that can follow," Henry Hu, professor of corporate and securities law at the University of Texas said.
"It also serves to remind people that no matter how much in legal fees they spend, even high priced lawyers can't guarantee people will stay out of jail."
Steep sentences expected
Lay and Skilling not only maintained their innocence but asserted that Enron was financially sound and brought down by unflattering news reports and a conspiracy of short sellers.
Their defence team argued that the nine former Enron employees who implicated who implicated Skilling and Lay were coerced to lie in order to avoid costly trials and potentially steep jail sentences.
Skilling has already posted a $US5 million ($A6.65 million) cash bond and has been released until sentencing.
Lay was told to sign a $US5 million ($A6.65 million) bond and Judge Sim Lake asked each of his children to co-sign the bond. He was also told to surrender his passport.
"Certainly we're surprised. I think probably more appropriately to say we're shocked," said Lay.
Lay, who is currently facing a maximum of 165 years in jail, said he still considers himself "a very blessed man" because he has the love of his wife and family and faith in God.
"Obviously as time goes on we'll have more things to say," Lay concluded.
When asked by a reporter whether he would ever be able to admit to himself that he had committed crimes, Skilling said "No." When asked why not, he responded "I didn't. We fought a good fight and we didn't get the verdict we wanted."
Government encouraged
The US government says it will hunt down corporate cheats as vigorously as street criminals after Enron's former chief executives were found guilty.
Deputy Attorney General Paul McNulty said the convictions showed that "no one, including the heads of Fortune 500 companies, is above the law".
"The message of today's verdict is simple -- our criminal laws will be enforced just as vigorously against corporate executives as they will against street criminals," he said in a statement.
Mr McNulty said the hard work of federal prosecutors and investigators had brought about a "tremendous win in bringing these important convictions".
"Lay, Skilling and their numerous co-conspirators perpetrated an elaborate scheme to mislead analysts and investors about Enron's true financial picture," he said.
"Their efforts to mislead the markets were protracted, deliberate and dishonest. At a time when the company was floundering, these defendants perpetrated a lie that Enron was a robust and growing company in a strongest financial condition it had ever been in.”
“And so this verdict encourages us," he said. "It encourages us
to continue to combat corruption, wherever we find it."