Believed to be acting on orders from Osama bin Laden and Ayman al-Zawahiri, Choudary, with Omar Bakri Muhammad, Choudary helped form an Islamist organisation, Al-Muhajiroun. The group organised several anti-Western demonstrations, including a banned protest march in London for which Choudary was summoned to appear in court. The UK government banned Al-Muhajiroun. Choudary was present at the launch of its intended successor, Ahlus Sunnah wal Jamaah. He later helped form Al Ghurabaa, which was also banned. Choudary then became the spokesman for Islam4UK. He has been denounced by mainstream Muslim groups, and has been largely criticised in the UK media.
A critic of the UK's involvement in the wars in Iraq (2003–2011) and Afghanistan (2001–2016), Choudary praised those responsible for the September 11 attacks and 2005 London bombings. He promotes the implementation of Sharia law throughout the UK, Poland and India. He marched in protest at the Jyllands-Posten cartoons controversy, following which he was prosecuted for organising an unlawful demonstration. During a protest outside Westminster Cathedral in 2006, Choudary told demonstrators that the Pope should be executed for insulting Islam.
On 6 September 2016, Choudary was sentenced to five years and six months following conviction for inviting others to support the proscribed organisation ISIS. He was released automatically on licence in October 2018.
houdary referred to the 11 September 2001 terrorists as "magnificent martyrs". In 2003 he said that al-Muhajiroun would "encourage people to fulfil their Islamic duties and responsibilities", although he also said that the group was a political movement and not responsible for individual actions. In 2004 he said that a terror attack on British soil was "a matter of time". He refused to condemn the 7 July 2005 London bombings, but accused the Muslim Council of Britain (who had) of "selling their souls to the devil". He blamed the 2013 murder of Lee Rigby, an off-duty British soldier, on British foreign policy.
Choudary has voiced support for the Muslim community in Somalia, who, he claims, have been "violated" by Christian-backed Ethiopians, and has also called for other members to fight jihad.
The Wall Street Journal describes Choudary as a supporter of "the fundamentalist strain of Islamic teaching known as Salafism". He believes in the primacy of Islam over all other faiths, and the implementation of Sharia Law, in its entirety, in the UK. In 2001 he stated that his allegiance is to Islam, and not a country. He believes that, for a true Muslim, "a British passport is no more than a travel document." In October 2006 he addressed an audience at Trinity College, Dublin to oppose the motion that "This house believes that Islamist violence can never be justified". In February 2008 the Archbishop of Canterbury, Rowan Williams, commented that "as a matter of fact certain provisions of sharia are already recognised in our society and under our law". Choudary responded by saying that Sharia "has to be adopted wholesale", and that "it will come either by embracing Islam because it is the fastest growing religion in the country, or by an Islamic country conquering Britain or by elements embracing Islam and imposing it."
In 2008 he spoke of the "flag of Sharia" flying over Downing Street by 2020, claimed that some Muslim families in east London were having "10 or 12 children each", and that hundreds were converting to Islam each day. Choudary has spoken against elements of the Christian faith. In December 2008 he posted a sermon on an Islamic website, in which he stated: "Every Muslim has a responsibility to protect his family from the misguidance of Christmas, because its observance will lead to hellfire. Protect your Paradise from being taken away – protect yourself and your family from Christmas".
In an interview with Iran's Press TV (which was subsequently posted online on 11 April 2013), Choudary stated "As Muslims, we reject democracy, we reject secularism, and freedom, and human rights. We reject all of the things that you espouse as being ideals ... There is nothing called a republic in Islam. When we talk about the shari'a, we are talking about only the shari'a. We are talking about rejecting the U.N., the IMF, and the World Bank."
In 2013 the British pressure group Hope not Hate presented a report which identified Choudary as "a serious player on the international Islamist scene", saying that although there was no evidence that he was directly responsible for instigating any terrorist plots, "he helped shape the mindset of many of those behind them" and "through his networks linked them up to terror groups and supporters across the world." Choudary dismissed the claims as "fanciful", saying that if they were true, UK security services would have arrested him.
In September 2014, Choudary described Abu Bakr al-Baghdadi, leader of the Islamic State of Iraq and the Levant, as "the caliph of all Muslims and the prince of the believers".
Secretly filmed by The Sun, Choudary said it is normal to take money from the kuffar (non-Muslim) and use it to fund jihad, which he called "Jihad Seeker's Allowance." Himself, he claimed more than £25,000 a year in benefits, £8,000 more than the take-home pay of some soldiers fighting the Taliban in Afghanistan, and totalling up to £500,000. Facing a court sentence for inciting terrorism, he wanted to move to the Islamic State, but explained that the reason was that it is a much better society in terms of welfare benefits and other factors