Shamima Begum, who joined the group of the Islamic State at the age of fifteen, will receive legal counsel to challenge the decision to revoke her British citizenship.
The 19-year-old, who left East London in 2015, was deprived of her citizenship in February after being found in a Syrian refugee camp.
Her family has previously announced that she will challenge the decision.
Foreign Minister Jeremy Hunt said that the idea of legal assistance for Ms. Begum had made him "very uncomfortable".
However, Hunt added that the UK is "a country that believes that people with limited resources should have access to the resources of the state if they want to question the decisions of the state."
Legal aid is a financial assistance granted by the taxpayer to those who are unable to afford legal representation, whether charged with a criminal offense or a victim seeking legal assistance from a lawyer ,
In recent years, availability in England and Wales has been severely curtailed.
Officials of the Legal Aid Agency, which is part of the Ministry of Justice, are responsible for deciding who receives legal assistance.
Previously, the BBC had reported that Ms. Begu's case had been approved, but the sources say it will be formally lifted in the coming days.
Expected legal aid refers to a case before the semi-secret Special Immigration Appeals Commission, which adjudicates cases in which the Home Secretary deprived a person of nationality for reasons of national security.
Cases before the Special Immigration Appeals Commission (Siac) are among the most complicated legal challenges the government can face.
This is due to the fact that it is usually a complex combination of MI5 intelligence reports that can not be disclosed to the complainant and a long-standing law to achieve a fair hearing.
It is not yet clear when the expected case will be heard, but the Siac process can take years. The granting of legal aid is not uncommon in these circumstances.
In the last decade, there have been many other people deprived of their citizenship because they are linked to the terrorism that was legally supported during the SIAC process.
Ms Begum left the United Kingdom in February 2015 with classmates of 15-year-old Amira Abase and 16-year-old Kadiza Sultana of the Bethnal Green Academy.
Ms. Begum was found in a Syrian refugee camp in February 2019 and said she wanted to return home.
Soon after, she gave birth to a boy named Jarrah. He died of pneumonia in March at the age of less than three weeks. She had two more children, who also died.
After the boy's death, Interior Minister Sajid Javid was criticized for having decided to withdraw Ms. Begum's British citizenship.
Three weeks before the death, Ms. Begum's sister, Renu Begum, wrote to Mr. Javid and asked him to help her bring the baby to the UK.
On Monday, the Daily Mail reported for the first time that legal aid had been granted following a request made on 19 March.
Mr Javid said that granting legal aid was a decision for mutual assistance organizations and that it was "no opinion of ministers".
Union leader Jeremy Corbyn argued that Ms. Begum has the right to seek legal assistance.
"She is a British citizen," he said. "She has the right to seek legal assistance if she has a legal problem like any other."
He added, "The key point of legal aid is that if you face prosecution, you are entitled to representation, a fundamental rule of law, a fundamental issue in any democratic society."
"No political decision"
Dal Babu, a former chief inspector of the Metropolitan Police and a friend of the family, said that Ms Begum should receive legal assistance to ensure that the correct process is followed.
He said to today's BBC Radio 4 program, "I think legal assistance is a principle of the British legal system."
According to the British Nationality Act of 1981, a person may be deprived of his or her citizenship if the Minister of the Interior is satisfied that this "is conducive to the public good" and does not render them stateless.
It was believed that Ms. Begum had Bangladeshi citizenship from her mother – although the Bangladesh Ministry of Foreign Affairs stated that she had been "mistakenly" identified as a Bangladeshi citizen.
The Liberty Libertarian said granting legal assistance in this case was "not only appropriate, but essential to ensure that government decisions are carefully considered".