Reid, also known as Abdul Raheem and Tariq Raja, was born a British citizen in Bromley, South London to Leslie Hughes who was of white English descent, and Colvin Robin Reed, whose grandfather was a Jamaican immigrant of African descent. When Reid was born, his father, a career criminal, was in jail for stealing a car. Reid left school at age 16, becoming a petty crook who was in and out of jail himself; the first time for assaulting an elderly woman. He served sentences at the Feltham Young Offenders Institution and at the Blundeston Prison. According to his father, Reid became depressed and blamed racism for some of his problems. His father advised him to convert to Islam, telling him that Muslims were more egalitarian and they got better food in prison. The next time Reid was incarcerated, (in 1995 for petty theft), he converted.
Upon his release from prison in 1996 he joined the Brixton Mosque, but later began attending the radical Finsbury Park Mosque in North London headed at that time by extremist cleric Abu Hamza al-Masri and described as "the heart of the extremist Islamic culture" in Britain. By 1998 Reid was voicing extremist views and may have fallen under the sway of "terrorist talent spotters and handlers" allied with Al Qaeda.
He spent 1999 and 2000 in Pakistan and trained at a terrorist camp in Afghanistan according to several informants. He may also have attended an anti-American religious training center in Lahore Pakistan as a follower of Mubarak Ali Gilani Reid then lived in various locales in Europe, communicating with an address in Peshawar, Pakistan, a city known for its Al Qaeda connections. In July 2001 he flew to Israel, passing through El Al's security, possibly a test of his ability to pass through an intensive security screening. On December 21, 2001, he attempted to board a flight from Paris to Miami but his boarding was delayed because his disheveled physical appearance was suspicious to screeners. He also did not answer all of their questions, and had not checked any luggage for the transatlantic flight. Additional screening resulted in his being re-issued a ticket for a flight on the following day. He returned to the airport on December 22, 2001 and boarded American Airlines Flight 63 from Paris to Miami, wearing his special shoes packed with plastic explosives in the hollowed out bottoms.