The 19-year-old has been advocating for girls' education since fleeing war-torn Syria in 2013.
“As a refugee, I saw what happens when children are forced into early marriage or manual labour – they lose out on education and they lose out on possibilities for the future,” said Ms Almellehan, recalling that when she fled, the only belongings she was able to take with her were her school books.
Ms Almellehan, is also the first person with an official refugee status to become an Ambassador for the United Nations Children's Fund.
Since fleeing her homeland, she had been living in Jordan for three years, before being resettled in the United Kingdom.
Za'atari camp experience
UNICEF says that it was during her 18 months in the Za'atari camp in Jordan that she began advocating for children's access to education, particularly for girls.
“Muzoon's story of bravery and fortitude inspires us all,” said Justin Forsyth, Deputy Executive Director of UNICEF, in the release, adding: “We are very proud she will now become an Ambassador for UNICEF and children around the world.”
In April this year, Ms Almellehan – dubbed 'the Malala of Syria' – travelled to areas affected by the Boko Haram conflict in the Lake Chad region where she met with children forced out of school due to the violence.

Syrian refugee and education activist Muzoon Almellehan the Kousseri internally displaced peoples site in the Lake Region, Chad, Source: UNICEF/Sokhin
An estimated 25 million children of primary and secondary school are out of school in conflict zones around the world, according to UNICEF.
For children living as refugees, only half are enrolled in primary school and less than a quarter are enrolled in secondary school.
Since 2010, less than 2 per cent of humanitarian funding has been spent on education.
UNICEF says some $8.5 billion is needed annually to close this widening gap.
UNICEF's celebrities
UNICEF has previously used celebrities to promote its causes.
Danny Kaye pioneered the role of Ambassador-at-Large in 1954; it was taken on by Audrey Hepburn and with many others following.

Danny Kaye Source: Mary Evans Picture Library