Several individuals — including two terminally ill people and a doctor — had brought the case before the court, demanding a ruling in the staunchly Catholic EU state.
“The decision consciously to take one's own life must be respected by the legislator,” court president Christoph Grabenwarter told reporters, while stressing the choice had to be made “freely, without any outside influence”.
Currently, assisted dying is punishable by up to five years in prison.
Austria's ruling conservative-green coalition government had called for existing legislation banning assisted suicide to be maintained, citing “potential abuses” if it were legalised.
Protagonists of legalisation say a ban encroaches on religious freedom to the extent it is based on Christian ethical considerations.
Elsewhere in Europe, euthanasia is legal in the Netherlands and Belgium but traditionally Catholic states such as Ireland and Poland are holding out against liberalisation.