In a statement Tuesday, lawyers for Tom Mortier said they brought their case to the European Court of Human Rights in Strasbourg after Belgian authorities declined to pursue it.
Robert Clarke, one of Mortier's lawyers, said there were some "deeply worrying" details about the case.
"This was a woman who was under the care of a psychiatrist and according to medical definition was a vulnerable person," Clarke said. "The state had a duty of care to protect her and it failed."
The court said it would now consider whether Belgium had violated two parts of the European Convention on Human Rights in euthanizing Mortier's mother.
Mortier's statement to the court alleges that Belgium failed to protect his mother's life and that there was no thorough or effective investigation into her death.
Mortier's mother, Godelieva De Troyer, 64, had struggled with depression for years. When her own doctor refused to approve her euthanasia request, she sought out other physicians, including Dr. Wim Distelmans, who also co-chairs Belgium's euthanasia review commission.
Mortier argued in his court statement that there was a troubling lack of oversight in the case, pointing out that his mother donated 2,500 euros ($2,860) to an association that Distelmans headed shortly before her euthanasia.
Last November, Belgian officials began investigating whether the psychiatrist who approved De Troyer's euthanasia request, Dr. Lieve Thienpont, was also responsible for the wrongful death of Tine Nys, who was diagnosed with Asperger's syndrome by Thienpont two months before she was euthanized. In addition to Thienpont, two other doctors are being investigated for "poisoning" Nys in 2010.
Some experts estimate that Thienpont has been involved in about a third of all euthanasia cases for psychiatric reasons in Belgium.
Many health experts — in Belgium and beyond — dispute whether mental health illnesses should be considered a valid justification for euthanasia.
In the 15 years since doctors were granted the right to legally kill patients in Belgium, more than 10,000 people have been euthanized. Only one case has previously been referred to prosecutors; that case was later dropped.
The European Court of Human Rights has notified Belgium of its decision to consider the case and has sent a list of questions to be answered in writing. A spokeswoman for the court said it was not known yet if the case might warrant a public hearing or when a judgment would be made.
This story corrects the woman's age at death to 64.