A court has ruled that Begum "cannot play any meaningful part in her appeal" from the Syrian refugee camp where she is currently.
A woman who had her British citizenship revoked after she left the country to join the so-called Islamic State (IS) has won the right to return to the UK to challenge the government's decision.
Shamima Begum left her parents' home in East London at just 15 in 2015 to travel to Syria to join IS.
She was found in a refugee camp in 2019 and asked to be allowed to return to the UK.
In response, then Home-Secretary Sajid Javid revoked her British citizenship, arguing that as both her parents had Bangladeshi passports, she could acquire citizenship there.
Begum appealed the decision.
The Special Immigration Appeals Commission (Siac) ruled earlier this year that stripping Begum of her UK citizenship was lawful because it did not make her stateless but said that she could "not have an effective appeal in her current circumstances".
The Court of Appeals upheld part of the Siac's ruling on Thursday, contending that "in her current circumstances" in the Syrian camp she "cannot play any meaningful part in her appeal, and that, to that extent, the appeal will not be fair and effective".
It thus concluded that she "should be allowed to come to the United Kingdom to pursue her appeal albeit subject to such controls as the Secretary of State deems appropriate".
Begum's family lawyer Tasmine Akunjee reacted to the Court of Appeal's decision on Twitter, writing: "Good sense prevails".
The Home Office described the ruling as "very disappointing".
"We will now apply for permission to appeal this judgment, and to stay its effects pending any onward appeal.
"The Government’s top priority remains maintaining our national security and keeping the public safe," it added.