The Court of Appeal ruling means she remains in Syria with no chance of return to the UK.
Begum left her home in London aged 15 in 2015 to travel to Syria to join Islamic State group. The now 24-year-old's lawyers brought a bid to overturn a 2023 decision at the Court of Appeal, with the Home Office opposing the challenge.
The Home Office argued the "key feature" of Begum's case was national security.
