The Bank of England reported the unusual trading pattern within 40 minutes and did not buy the gilts as part of QE.
"Stevenson's abuse took advantage of a policy designed to boost the economy with no regard for the potential consequences for other market participants and, ultimately, for U.K. tax payers. He has paid a heavy price for his actions," Tracey McDermott, the FCA's director of enforcement said in a press release.
The trader's actions were described as "particularly egregious" by the authority. When the Bank of England reintroduced QE on 10 October 2011, Stevenson "significantly increased" his holding of gilts with the "express intention" of inflating the price, the FCA said.
(Read more: Bank of England in shake-up, Posen attacks values)
Had the Bank of England bought Stevenson's bonds, it would have accounted for 70 percent of the £1.7 billion allocated to QE on that day. Any losses would have been compensated by the government and paid for by the taxpayers.
"We agree with the FCA's decision to sanction Mr. Stevenson and are pleased to note that neither Credit Suisse nor any other employed individuals have been found at fault," a spokesperson for Credit Suisse said in an emailed statement. Stevenson was removed from trading by the bank in October 2012 and left the company in December last year.
"The bank cooperated fully with the investigations into this matter by the Bank of England and Financial Conduct Authority."
—By CNBC's Arjun Kharpal. Follow him on Twitter