Maria Sharapova, a five-time Grand Slam champion and one of the world’s highest-paid female athletes, was suspended for two years Wednesday when an International Tennis Federation tribunal ruled that she unintentionally committed a doping violation.

Sharapova announced in March that she tested positive for meldonium on Jan. 26 at the Australian Open and began serving a provisional suspension. Meldonium, a heart medication that is said to improve blood flow and allow athletes to recover faster, was added to the World Anti-Doping Agency’s prohibited list on Jan. 1 after the agency monitored its use for a year.

Sharapova, 29, said she had been taking Mildronate, whose active ingredient is meldonium, since 2006 to help manage a variety of health problems and was not aware that the drug had been banned.

After a hearing May 18 and 19, a three-member tribunal appointed by the I.T.F. ruled that while Sharapova’s doping violation was not intentional, “she does bear sole responsibility for the contravention, and very significant fault, in failing to take any steps to check whether the continued use of this medicine was permissible.”

Sharapova faced a suspension of up to four years if the tribunal decided her doping violation was intentional. Because of her prompt admission of her violation, the I.T.F. said, the suspension will be backdated to begin on Jan. 26, and she will be eligible to return at midnight on Jan. 25, 2018.

Sharapova is the highest-profile tennis player to have a positive doping test. She said in a statement released on her Facebook page that she would appeal the suspension through the Court of Arbitration for Sport.

“I cannot accept an unfairly harsh two-year suspension,” she said. “The tribunal, whose members were selected by the I.T.F., agreed that I did not do anything intentionally wrong, yet they seek to keep me from playing tennis for two years.”

A four-year suspension could have been career ending, but if her ban is upheld, Sharapova, who has missed long periods on the tour because of injuries and has seen her ranking fall to No. 26, would be 30 when she returned to a sport in which Williams and Roger Federer remain top players in their mid-30s.

The International Tennis Federation appointed a three-member tribunal to investigate the positive doping test for meldonium by Sharapova.

A lengthy doping suspension could harm Sharapova’s well-known brand, but she received support Wednesday from Nike, which along with other sponsors had suspended its relationship with her after the positive doping test was revealed in March.

“The I.T.F. tribunal has found that Maria did not intentionally break its rules,” the company said in a statement. “Maria has always made her position clear, has apologized for her mistake and is now appealing the length of the ban. Based on the decision of the I.T.F. and their factual findings, we hope to see Maria back on court and will continue to partner with her.”