Before the judge's ruling, Fastow told the court, "I wish I could undo what I did at Enron but I can't."
U.S. District Judge Kenneth Hoyt could have sentenced Fastow to up to 10 years in prison but was more lenient because of Fastow's cooperation with government authorities and his family's distress since the Enron fallout.
Fastow's wife Lea pleaded guilty to a misdemeanor tax crime and served a year in prison.
"What moves the arm of justice is mercy," Hoyt told Fastow. "You were drunk on the wine of greed ... [but] you had a double portion, in that your wife shared in that [punishment]."
Fastow helped prosecutors at the trials of former colleagues Kenneth Lay and Jeffrey Skilling, testifying that both were complicit in the fraudulent accounting practices that caused Enron's downfall.
After his conviction in May, Lay died of a heart attack; his lawyers are currently trying to erase his convictions. Skilling, who was also convicted in May of conspiracy and fraud, will be sentenced in October.
In recent weeks, Fastow had aided Enron shareholders' lawyers in recouping money from banking institutions, all of which have denied any impropriety in separate court filings.
Hoyt also ordered Fastow to two years of supervised release after serving his sentence.
The court did not issue any fines as Fastow had already given back $24 million and his family had surrendered more than $5 million.
In the fallout of Enron's December 2001 collapse, in which thousands of jobs were lost and $60 billion dollars in market value disappeared, Fastow was indicted on 98 counts, including fraud, conspiracy and insider trading. When entering his guilty plea, he also admitted to hide Enron's debt and inflate profits.