The woman, Alda Gross, had filed a complaint saying doctors refused to help her end her life because of the suffering of old age, as she was not suffering any clinical illness.
In a ruling in May last year, the court ruled "that Swiss law was not clear enough as to when assisted suicide was permitted."
Only eight months later, in January this year, it emerged that Gross had in fact died in 2011 after a medical practitioner in Switzerland prescribed her a lethal dose of sodium pentobarbital.
Not even her lawyer was aware that she had died a year after filing her complaint at the court in November 2010.
"The court came to the conclusion that the applicant had intended to mislead the Court on a matter concerning the very core of her complaint," it said in a statement.
"In particular, she had taken special precautions to prevent information about her death from being disclosed to her counsel, and thus to the court, in order to prevent the latter from discontinuing the proceedings in her case."
Gross, born in 1931, had on several occasions been refused the prescription required to obtain the lethal drugs to end her life.
"She submitted that she was becoming increasingly frail and was unwilling to continue suffering the decline of her physical and mental faculties," said the court.
Swiss courts had previously ruled that Gross did not fulfil the conditions set up by the Swiss academy of medicine as she was not suffering from any terminal disease.
However, after taking the matter to the Strasbourg-based rights court she pushed on in her efforts to get the prescription, and eventually succeeded.
Death deliberately concealed
It was the Swiss government, seeking an appeal, which eventually discovered Gross was already dead.
Her lawyer told the court he was unaware as he had only had contact with her via a retired pastor who volunteered as a spiritual adviser with the assisted suicide association EXIT.
The pastor claimed he had followed Gross' wishes not to tell her lawyer of her death as she wanted "the proceedings in her case (to) continue for the benefit of other people in a similar situation."
Switzerland has long allowed assisted suicide, although patients have to be able to take the lethal dose themselves. Euthanasia, or the direct killing of a suffering person, remains illegal in the country.
This has led to a boom in so-called "suicide tourism", as Switzerland is the only country that allows nationals from other countries to use their services.
Debates on assisted dying have recently gripped both France and Britain.
Few countries regulate assisted suicide, or euthanasia, and in many it is a punishable crime to help someone end their life, even if they are suffering severe and incurable pain.
EXIT announced in May it would extend its services to help elderly patients who are sick, but not terminally ill, end their lives.