Mullings, 30, who won a gold medal in the 4x100 metres relay at the 2009 world championships in Berlin, tested positive for testosterone in 2004 and for the banned diuretic furosemide in 2011.
The sprinter, who missed the Athens Olympics because of the first ban, questioned the methods which led to the results of both tests, but CAS rejected his arguments.
"The athlete argued that there were problems with the 2004 positive test meaning it should not be counted as a first sanction for a doping offence," said CAS.
"He argued further that the laboratory results of the 2011 test were unreliable and that the disciplinary proceedings were flawed."
CAS said proceedings were delayed as it collected evidence from both tests.
"The CAS panel..... considered that the athlete had not presented any basis to challenge the testing procedure of the 2011 sample," said the verdict.
"Furthermore, while Mullings has attempted to raise suspicion about his first violation, the CAS panel did not find that the circumstances surrounding the first offence warranted a more lenient sanction."
Mullings tested positive for furosemide after finishing third in the 100 metres final at the Jamaican national trials in June.
- Sports & Recreation