Dubbed the White Widow, Lewthwaite is wanted in connection with an atrocity in Kenya, her alleged role in bomb-making factories and terrorist activity in Yemen.
Such is the perceived threat posed by Lewthwaite, a dedicated unit of the elite SAS has reportedly been tasked with finding her.
While Northern Ireland is no stranger to homegrown terrorism, Samantha Lewthwaite's story is unique.
Born to a British soldier from England and a Northern Irish Catholic mother, Lewthwaite spent her early years in the family's home in Banbridge's Whyte Acres estate.
The family moved to Aylesbury in Buckinghamshire but in 1995 Lewthwaite's parents Andy and Christine separated.
Distraught, Lewthwaite spent more time with Muslim neighbours and was apparently drawn to the faith by their close family ties. Then, at the age of 17, she converted to Islam, marking her religious conversion by changing her name to Sherafiya and swapping jeans and jewellery for a traditional long gown.
In 2002, she married Jermaine Lindsay in an Islamic ceremony at a house in Aylesbury.
The pair met on an Islamic chatroom while she was studying religion and politics in London and he was working as a carpenter. Neither of her parents attended the wedding.
Days after her husband blew himself up on a London Underground train in July 2005, killing 26 people, pregnant Lewthwaite tried to distance herself from the attacks. She described the terrorist bombings as "abhorrent".
In a statement she explained: "Jamal is accountable for his actions 100% and I condemn with all my heart what he has done."
In 2009, Lewthwaite and her children disappeared from the UK.
She resurfaced two years later after travelling to Kenya using a false passport.
The Kenyan authorities issued a photograph of a woman wanted for questioning after a bomb factory was discovered at a house in Mombasa. The picture on it was that of Lewthwaite.
Police said they were tipped off that terrorists were planning a bombing campaign on shopping centres and hotels. Last year, Kenyan police revealed they were searching for her on suspicion of taking part in a grenade attack on a bar which had been packed with tourists watching an England football match. Three people were killed and 25 injured.
Lewthwaite is believed to be in the inner circle of al-Shabaab, an al-Qaida-linked group, the name of which translates as 'the people'.
It is understood she controls the group's finances and is a vital conduit between al-Qaida groups in Pakistan and east Africa.
Al-Shabaab is a militant group fighting to create an Islamic state in Somalia.
From innocent schoolgirl to a worldwide jihadist
December 5 1983: Born to parents Andrew and Christine. They lived briefly in Banbridge while Andrew, a British Army soldier, was serving in Northern Ireland. They later moved to Aylesbury in Buckinghamshire.
1995: Mr and Mrs Lewthwaite split. Friends say Samantha was badly affected by the break-up.
2001: Having started an A-Level in religious studies, she converts to Islam.
2002: She marries Jermaine Lindsay in an Islamic ceremony in a house in Aylesbury.
2004: Their first child, a son, born.
September 2004: Samantha meets Mohammad Siddique Khan, the ringleader of the July 7 attacks.
July 7, 2005: Lindsay detonates a bomb on a train between King's Cross and Russell Square, killing himself and 26 passengers.
July 2005: Samantha calls police to report her husband missing.
September 2005: Samantha gives birth to her second child, a daughter. Lindsay is the father.
July 2009: She gives birth to a third child, a boy. It is not known who the father is.
August 2011: Travels to Kenya on a false South African passport.
2012: Kenyan police reveal they are searching for Samantha on suspicion of taking part in a grenade attack on a Kenyan bar.
In March, notes emerge supposedly written by Samantha with plans for a book about being the wife of an Islamic holy warrior.
In July, reports emerge that Samantha is attempting to recruit all-female terror cells
2013: In March Mombasa Magistrates Court hears Samantha was behind an armed mission to break an accomplice identified as Jermaine Grant out of custody
September: Habib Ghani, who is believed to be Samantha's second husband, is murdered.
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