An independent Tennis Australia (TA) tribunal hearing handed down the ban this week, making the South Australian the first Australian sportsperson in history to be suspended for using the party drug and the first Australian tennis player to receive a drug sanction.
But Mousley, Australia's top ranked junior male, is considering an appeal.
The ban will be backdated to May 30 this year, when the 18-year-old accepted a provisional suspension.
That means he will be eligible to compete again on May 30 next year.
Lawyers for the Adelaide teenager had argued for a three-month ban and told the hearing the player had not taken the drug with the intention of enhancing his performance.
They told the hearing Mousley attended an 18th birthday party with fellow junior tennis players Jason Scott and Li Tu on Friday, March 28.
Mousley admitted to purchasing one ecstasy tablet at the party because he "wanted to be active and dance to the music" and because he was feeling down.
Tu and Scott both declined offers to take the drug.
Mousley was subsequently tested by an ASADA official after his opening round match of qualifying for a Futures event at Melbourne Park on the Sunday morning of March 30 — about 36 hours after he had taken the tablet.