Born Marie Fadia Laham in Beirut, Lebanon, her Palestinian father had fled Nazareth at the time Israel was created in 1948 while her mother was Lebanese. After her education by French nuns, she became a hippie for 2 1⁄2 years and, by her own admission, smoked marijuana while travelling in Europe, India and Nepal. While in Nepal she was overcome by God's unconditional love, and a revelation in which "God gave me a glimpse of the glory he has reserved for those who are saved." She then became a nun in the Carmelite order in 1971, and worked to help displaced families from Lebanon's civil war.
Mother Agnes gained the consent of the religious authorities to work with the Melkite Greek Catholic Church in 1992, and moved to Syria about two years later with the objective of restoring the monastery. Mother Agnes said at an event in San Francisco during her American tour in 2013: "I used to hate Syrians who came to Lebanon to bomb us every day" during the country's civil war, but "then the Lord called me to Syria to a blessed adventure to restore an ancient monastery that was in ruins" and underwent a "conversion" after which she "learned never to hate anyone".
Mother Agnes Mariam has been alleged to have been involved in a Syrian government plot to kill the French journalist Gilles Jacquier who lost his life in Homs during 2012. A book written by his widow and two colleagues, in which the accusations are made, has led Mother Agnes to sue for defamation. She has asserted that in Homs 80,000 Christians have become displaced by opposition groups, and has also said that the majority of fighters are from outside Syria. The latter claim has been disputed. Interviewed by The Australian in October 2012, Mother Agnes said the rebellion "steadily became a violent Islamist expression against a liberal secular society."
Mother Agnes attempted to prove that Syrian opposition activists fabricated the videos showing victims of the Ghouta chemical attack in Damascus on 21 August 2013. She has no formal training in analysing video evidence or the use of chemical weapons, but compiled a 50-page report in her hotel room which she subsequently issued. Sergey Lavrov, the Russian foreign minister, has used her claims to cast doubt over whether Assad's forces had been responsible for the Ghouta chemical attack, and Mother Agnes has been given time on the Russian RT station to convey her opinions. Peter Bouckaert, emergencies director of Human Rights Watch, has said that her claims are entirely false, and that HRW has found no evidence that the videos were staged. In 2013, rebels near the monastery warned her that extremist fighters wanted to abduct her, and helped her flee. Mother Agnes acted as government liaison during the evacuation of Moadamiyah (then under siege) at the end of October 2013. While up to 1,800 women, children and others were freed, according to rebel spokesman Quasi Zakarya, about 300 men were arrested by the government and have been forced to join the Syrian army. According to a well placed government source she was in daily contact with Ali Mamlouk, chief of Syria’s National Security Bureau, and Jamil Hasan who heads the country's Air Force Intelligence. According to Raya Jalabi in The Guardian: "Asked whether she considers Hezbollah and Iran – Shia entities which support the Assad regime – to be complicit in the fabric of foreign sectarian forces inside Syria, she said no, as 'Hezbollah isn’t coming in as a religious force, and is not committing crimes of a religious nature.'
In late 2013, she toured the United States and visited Europe presenting her version of events in Syria. Organised by the Syria Solidarity Movement, a non-profit organisation based in California, it was planned for Mother Agnes to speak at venues, mainly churches, on the west and east coasts.
In November, she withdrew from speaking at the forthcoming British Stop the War Coalition's annual conference on 30 November after two participants, Jeremy Scahill and Owen Jones, had decided not to speak at the meeting if it meant sharing a platform with Mother Agnes. The commentator James Bloodworth, in his blog for The Spectator, described her as having a "pro-Assad take" on events in Syria. Father Paolo Dall'Oglio, a Jesuit priest on the side of the Syrian opposition has said Mother Agnes "is very careful when she speaks and this is – and I wish to repeat and emphasize this – nothing more than a clever example of the lying, manipulative work of the Syrian regime. Sister Agnes states she is the head of a movement that is not present in the country and is called Musalaha or "Reconciliation". This is a serious problem because her interpretation of events is selective and she believes the revolution is terrorism!"