She was born as Antoinette “Toni” Avril Gardiner in Chelmondiston, Suffolk, England and raised as a Christian in the United Kingdom. Her parents were Walter and Doris Gardiner. She was educated at Bourne School, for a time, in Malaysia and was reportedly an excellent field hockey player. She was in school in the Asian country while her father, a high-ranking Army officer, was stationed there; the school would close after British forces left the country. 

Toni would work as a secretary in Stratford in the 1960s during her father’s time being stationed in Long Marston. He would eventually be sent to Jordan as a military adviser on water conservation; it was during this period that she met King Hussein when she was 19-years-old. A biography by Roland Dallas said that she remarked to the King at a costume party when they met, “It makes you look rather scruffy, Your Majesty!” Toni would work on the set of the movie Lawrence of Arabia (some of the desert scenes were filmed in Jordan), as well during this time. 

On 25 May 1961, the couple married, and she took the name of Muna after converting to Islam from Christianity (although rumours persisted that she never actually converted). She was known as Her Royal Highness Princess Muna al-Hussein after the birth of their first child. Together, they had four children: (then Crown Prince) King Abdullah II (b. 1962), Prince Faisal (b. 1963), and twins, Princess Aisha (b. 1968) and Princess Zein (b. 1968).