The sentencing guidelines called for five years of prison time for the defendant, 40-year-old Kareem Serageldin, The New York Times reported.
Judge Alvin Hellerstein said he was lenient due to the atmosphere at Credit Suisse Group.
"He was in a place where there was a climate for him to do what he did," he said. "It was a small piece of an overall evil climate inside that bank and many other banks."
Serageldin led a mortgage-based securities group that made hundreds of millions of dollars for the bank as the housing market soared, the Times reported.
But federal authorities, who began their investigation in 2008, discovered that the team had mismarked its portfolio.
Prosecutors argued that Serageldin did so to increase his bonus.
The defendant apologized for his actions during his sentencing Friday.
"This is the worst day of my life," he told the judge. "I am terribly sorry for what I have done."