The European Court of Human Rights (ECHR) has refused an application by 12-year-old Archie Battersbee's parents to postpone the withdrawal of his life support.
Archie has been kept alive by ventilation and medication since he was found unconscious at home in Southend, Essex, on 7 April.
His mother Hollie Dance believes that he may have been attempting an online challenge when he suffered brain damage.
Doctors were to switch off his life support at 11am on Wednesday, but they waited on the ECHR's decision after Ms Dance and Archie's father Paul Battersbee made a last-minute bid to the Strasbourg-based court.
His parents submitted an application to the ECHR on Wednesday morning, just a few hours before Barts Health NHS Trust had been expected to end the life support.
In a number of cases at the UK's highest courts, the parents challenged the decision of doctors at the Royal London Hospital, who said that it's "highly likely" Archie is brain-stem dead and it's in his best interest for the life support to end.
But shortly after 6.30pm, the ECHR said it refused the parents' request, adding that it would not "interfere with the decisions of the national courts to allow the withdrawal of life-sustaining treatment from (Archie) to proceed".
Following the ECHR's decision, Ms Dance said it was "another heart-breaking development".
In a statement, she said: "The NHS, the government and the courts in this country and in Europe may have given up on treating him - but we have not.
"The whole system has been stacked against us. Reform must now come through Charlie's Law so that no parents have to go through this.
"In a worst-case scenario, we want to take Archie to a hospice, but the hospital has said that we cannot do that despite previous promises.
"We have been told all along that this is all about Archie dying with 'dignity'. Yet we're told we cannot take him to a hospice where it's quiet and we can spend time with him as a family without the chaos at the hospital. We will fight to the end for Archie's right to live."
On Tuesday, Ms Dance announced that the family would apply to the ECHR. It came after the Court of Appeal ruled on Monday that Archie's treatment should not continue beyond noon on Tuesday and the Supreme Court backed its decision.
The judges said that they have "great sympathy" for Archie's parents but that there's "no prospect of any meaningful recovery".
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