The Serbian, who will not be able to play again until July 15 next year, had initially been banned for 18 months but had argued the punishment should be overturned.
Troicki was given the initial punishment in July by an International Tennis Federation anti-doping tribunal after refusing to give a blood sample during the Monte Carlo Masters in April.
The decision comes 11 days after Croatia's Marin Cilic had his nine-month ban for failing a doping test reduced to four months, clearing him to play again.
In a statement, CAS said it determined Troicki "had committed a doping offence, but that his fault was not significant," and that 12 months was the minimum he could serve in such a situation in accordance with ITF anti-doping rules.
At the centre of the case is a disagreement between the player and the doping control officer (DCO) over what happened when he was selected to be tested in Monte Carlo.
Troicki has always insisted the officer told him it would be okay to miss the test because he was feeling unwell and has a severe phobia of needles.
But the doping official denied Troicki's version of events and the ITF tribunal agreed she had given no such assurance.
In a statement released through his manager, Troicki said: "I hoped that the most difficult period of my career and of my life would be over, and I really trusted the judges I met in Lausanne. I had the feeling that they were really looking for the truth and that they had found it during the hearing.
"Now this decision puts an end to my dreams of being a top player, of reaching the ATP finals and fighting against the best in the world. I worked my entire life for it, and it has been taken away from me in one afternoon by a doctor I didn't know.
"Regarding the TAS (CAS) I can only say that they are humans, and they probably didn't have the courage to go against the ITF releasing me and putting ITF in a bad situation. I am sure they feel bad about it, but in the end they will all go back to their jobs tomorrow [Wednesday], including (DCO) Doctor Gorodilova, and I won't.
"I thank everyone who has supported me so far - Novak (Djokovic), Janko (Tipsarevic), my family, my team and everyone who truly believes I am innocent. I won't forget it.
"I have no idea about what to do now or where to go. I hope somehow I will be able to fight back."
The ITF tribunal praised Dr Gorodilova as "conscientious and cautious" but the CAS panel said she "should have informed the player in clearer terms of the risks caused by his refusal to undergo a blood test".
The statement continued: "There was no suggestion that Mr Troicki intended to evade the detection of a banned substance in his system."
Troicki, whose ban had originally been due to run until January 2015, had hoped to be cleared to play for Serbia in the Davis Cup final later this month.
The 27-year-old has received a lot of support from his fellow players, especially countryman and Davis Cup team-mate Djokovic.
Talking about the case in Beijing last month, Djokovic accused the doping control officer of lying.
He said: "I don't see why they're keeping him suspended. For what? For failing to provide the blood test? He said to the lady that day that he's not feeling well. 'Can I provide (a sample) tomorrow?' She said, 'Yes, if you write a report'.
"He wrote the report, and the next thing you know she's failing to say the truth in the court. She was saying that he was convincing him, that it took her 20 minutes to walk from anti-doping office to the ATP office in Monte Carlo, which is 20 metres. So she was lying a lot. That's very bad for our sport."
Troicki reached a career-high ranking of 12 in 2011 after reaching the fourth round of the French Open, where he led Andy Murray by two sets to love before eventually losing in five.
In giving his reaction to the verdict, ITF president Francesco Ricci Bitti expressed his disappointment at the criticism of the doping control officer.
The CAS panel were critical of Dr Gorodilova for allowing the confusion that led Troicki and his coach Jack Reader to become convinced he would not receive any punishment for missing the test.
Ricci Bitti said in a statement: "We respect the ruling of the Court of Arbitration for Sport, who confirmed the decision of the independent tribunal that Viktor Troicki is guilty of an anti-doping violation, although they reduced the penalty to one year.
"What is harder to accept is criticism of doping control officers, who perform a difficult role."
It will surely be a source of private frustration to the ITF that bans in two high-profile cases have been reduced, and Ricci Bitti added: "We should all remember that exactly one year ago anti-doping programmes around the world were under scrutiny.
"This reinforced the need to be vigilant and apply the rules strictly, something that we and our partners in the Tennis Anti-Doping Programme strive to do to keep our sport clean."