The Belgian law on Euthanasia, in effect since 2002, includes the following preconditions: The patient has to be of sound mind and has to express his or her well-considered request voluntarily and under no duress. The patient's medical situation has to be desperate and resulting in constant and unbearable physical or psychological suffering caused by an accident or a severe and incurable illness and which cannot be alleviated. Due to an amendment passed in 2014 the criteria concerning legal age and, in the event of an under-age patient, maturity (“mineur emancipé”) have ceased to exist. In principle the right to active euthanasia is now accessible to patients of all ages while, once a minor requests euthanasia, additional restrictions apply (see also the module "Euthanasia for minors").

The killing on request performed by a physician is legal only if a certain procedure is adhered to: the physician has to inform the patient about his or her state of health, life expectancy and the available therapeutic and palliative options. The patient and the physician have to be convinced that there is no other "reasonable solution" for the patient. In a sequence of discussions with the patient over a suitable period of time the physician has to seek reaffirmation that the patient's physical and psychological suffering is truly permanent and the patient's death wish is persistent. Concerning the question whether the physical or psychological suffering is permanent, unbearable and beyond palliation a second, independent specialist has to be consulted. The wish to die has to be put in writing and signed by the patient's own hand. If the patient is incapable of doing so the request to die may be written down by a person of the patient's choice in the presence of the physician. This third person must not have any material interest in the death of the patient. If the natural death of the patient is not pending, i.e. will not occur within the foreseeable future, at least one month has to elapse between the written request to die and the performance of the killing on request.

Adult patients or minors of a comparable legal status ("emancipated minors") may formulate a living will covering the case in which they may no longer be able to express their wish. This living will may call for a physician to "carry out euthanasia" if due to a severe and incurable impairment as a consequence of an accident or a disease, the patient is unconscious and this state is irreversible, according to current medical knowledge. The living will may contain a list of trusted third parties to be included in the decision on the assumed will of the patient. If the patient is permanently incapable of formulating such a request, he or she may appoint a third person who has no material interest in the death of the patient. A physician who performs a killing on request on the basis of a living will made by an incurable and irreversibly ill and unconscious patient acts legally, if he or she adheres to certain procedures. Among those are the obligation to consult a second physician in the assessment of the patient's medical situation and to include the third party laid down in the patient's living will in the process of establishing the patient's assumed wish.

Any mercy killing has to be registered with and assessed by the "Federal Control and Evaluation Commission". The Commission has to judge whether the conditions and the procedures laid down for a legal killing on request are fulfilled. If two thirds of the 16-member commission (8 physicians, 4 members of the legal professions and 4 other professionals dealing with problems concerning the terminally ill) come to the conclusion that the preconditions are not fulfilled, the case has to be referred to the state attorney.

The Belgian National Bioethics Committee initially published its opinion on euthanasia in 1997. In 1999 the committee published another opinion specifically on euthanasia with regard to persons unable to give their consent.