The 24-year-old, currently ranked 24th in the world, has had the ban back-dated to May 1 this year, meaning he will be able to return to action on February 1, 2014.
Cilic's doping violation came when he tested positive for the stimulant nikethamide at the Munich Open in May.
"The International Tennis Federation announced today that Marin Cilic has been found to have committed an Anti-Doping Rule Violation under Article 2.1 of the Tennis Anti-Doping Programme (presence of a Prohibited Substance in a Player's Sample)," a statement confirmed.
Cilic, a former number nine and 2010 Australian Open semi-finalist, provided a urine sample during the Munich event and a WADA-accredited laboratory in Montreal found it to contain nikethamide, which is banned under section S6 (Stimulants) of the 2013 WADA List of Prohibited Substances and Prohibited Methods.
The Croatian, who said he would appeal his ban to the Court of Arbitration for Sport, claimed he was unaware that Coramine tablets he bought contained nikethamide, for which he did not hold a valid Therapeutic Use Exemption.
"The substance in question originated from a glucose tablet purchased at a pharmacy in France. Unbeknownst to me, the glucose tablets contained a substance that is banned in competition," Cilic said in a statement.
"I wish to emphasise that I have never knowingly or deliberately taken any banned substances in my life and that I am opposed to any use of performance-enhancing substances in sport."
An Independent Tribunal agreed that Cilic ingested the nikethamide inadvertently as a result of taking the tablets and did not intend to enhance his performance in doing so.
Therefore he met the preconditions of Article 10.4 of the programme, which entitles him to a reduction of the period of ineligibility based on an assessment of his fault.
As well as the ban "it was also determined that Mr Cilic's results at the 2013 BMW Open event should be disqualified, with resulting forfeiture of the ranking points and prize money that he won at those events.
"Mr Cilic's results subsequent to the BMW Open (in Munich), up to the time that he accepted a voluntary provisional suspension are also disqualified, and the ranking points and prize money forfeited. A fully-reasoned decision will follow in due course."
Following the Munich Open, Cilic was knocked out of the French Open in the third round by Viktor Troicki, who coincidentally was banned in July for 18 months for failing to provide a blood sample at the Monte Carlo Masters in April.
He then reached the final at Queen's where he lost to Andy Murray before withdrawing from Wimbledon, where he was seeded 10th, prior to his second-round match against Kenny de Schepper with a knee injury.
Cilic will miss the Australian Open while serving out the latter stages of his ban.