The court backed complaints by a group of terminally ill patients and doctors who challenged the law that made "commercial promotion of assisted suicide" a criminal offence.
Assisted dying had been legal.
But the law change prompted terminally ill people to go to Switzerland and the Netherlands to end their lives.
Advice centres that operated until 2015 had to stop working because of the risk of a jail sentence for promoting suicide.
The law was aimed at stopping groups or individuals creating a form of business, by helping people to die in return for money. In practice it meant a ban on providing any type of "recurring" assistance.