McCann was born and has lived most of his life in Derry. Raised Catholic, he attended St. Columb's College and is prominently featured in the documentary film, The Boys of St. Columb's. He later attended Queen's University Belfast, where he was president of the Literary and Scientific Society, the university's debating society.
As a young man he was one of the original organisers of the Derry Housing Action Committee (DHAC), a radical campaign group focusing on access to social housing. DHAC organised, in conjunction with the Northern Ireland Civil Rights Association (NICRA), the second civil rights march in Northern Ireland. This march, which took place on 5 October 1968, is generally seen as the birth date of the Northern Ireland Civil Rights Movement. His political contemporaries included Bernadette Devlin, for whom he served as an election agent. He stood for election in the Foyle constituency at the 1969 Northern Ireland general election for the Northern Ireland Labour Party, placing third with 1,993 votes (12.3% of the total).
He was tried (as one of the so-called Raytheon 9) in Belfast in May–June 2008 over alleged damage caused during the 2006 War on Lebanon to a facility operated by multinational arms company Raytheon in Derry. The jury unanimously acquitted McCann, and all the other defendants, of charges of criminal damage to property belonging to Raytheon. The jury had heard that the groups's actions were prompted by repeated bombing of Lebanese property in which numerous civilians died and the wish to protect those lives and that property from being attacked by Israeli forces with weapons, weaponry systems and missiles supplied by Raytheon. The judge dismissed charges of affray after hearing the prosecution evidence. However, McCann was convicted of the theft of two computer discs, for which he received a 12-month conditional discharge.
When Raytheon staff returned to the offices they alleged that some of their desks had been urinated on and also had human excrement smeared on them. In a statement outside the court McCann said: "[We] have been vindicated. ... The jury have accepted that we were reasonable in our belief that ... Israeli ... Forces were guilty of war crimes in Lebanon in the summer of 2006. The action we took was intended to have, and did have, the effect of hampering or delaying the commission of war crimes".
His appearance at the funeral of former PIRA volunteer, Old Bailey bomber, and republican activist Dolours Price, and a tribute he paid to her, was criticised by a son-in-law of Jean McConville, who was kidnapped, tortured and murdered by the PIRA. Price was suspected of being one of the paramilitaries who took part. McCann explained that her family had asked him to speak at her funeral. He said: "I don't think I said anything at Dolours Price's grave that contradicted that [calling McConville's murder 'a horrible and unforgivable act'] ... The point I had in mind, the point I was making, was there are some people deeply implicated in the cruel murder of Mrs McConville who appear not to be undergoing any inner turmoil. They appear to find it very easy to handle the knowledge of their own involvement in that murder".
He was elected as an MLA for Foyle in 2016 but was defeated just 10 months later
McCann attracted criticism from Sinn Féin and pro-European activists for supporting Brexit in an area with the 4th highest remain vote (out of approximately 400 counting areas) in the whole of the United Kingdom.
McCann currently writes for the Belfast Telegraph, The Irish Times and the Derry Journal. He has written a column for the Dublin-based magazine, Hot Press, and is a frequent commentator on the BBC, RTÉ and other broadcast media. He worked as a journalist for the Sunday World newspaper and contributed to the original In Dublin magazine, among others.
Much of his journalistic work reflects what he himself describes as a "shuddering fascination" with religion which, when coupled with his profound skepticism, has made it a topic to which he has often returned.
In March 2008, McCann spoke with National Public Radio in the U.S. about the solidarity between the Catholic civil rights movement in Northern Ireland and the Civil Rights Movement in the U.S.
In March 2014, following Crimea's referendum on joining Russia, McCann had a piece published in The Irish Times on the situation there. He commented: "After six years in office, Obama believes he has a right to invade anywhere, bomb anything, kill anybody whose jib the CIA doesn't like the cut of, irrespective of national or international law or, indeed, of the provisions of the US constitution. And now he lectures Putin on the necessity of 'respecting international law'. He has a nerve." McCann referred to "a cable summarising a discussion in Paris in September 2009 involving Philip Gordon, assistant US secretary of state for EU and Eurasian affairs and a group of French diplomats, including Jean-David Levitte, French ambassador to the US from 2002 to 2007."
McCann noted: "Under “Nato's Enlargement and Strategic Concept”, Levitte declared president Nicolas Sarkozy's position was that Ukraine's destiny lay within Nato but that it would be unwise to push the case just then for fear of antagonising Russia – and because a majority of the Ukrainian people appeared to be against the idea." He added: "It has virtually been ignored in the Western media that the EU offer of economic assistance to Ukraine last December included a condition that Kiev align its forces with Nato – a halfway-house staging post on the road to full Nato membership. It was this provision that deeply alarmed the Putin regime, which in turn sparked angry demonstrations in Kiev against the pro-Russian government of Viktor Yanukovich and its US-assisted replacement by a mixum-gatherum of groups, including anti-Semitic neo-fascists."
In the same piece he wrote: "Vladimir Putin may run a vicious regime but the people of Crimea have a right to be accepted as Russian if that's what they want, which evidently they do", and added: "Putin is right that the main motivation of the US and Nato has been to encircle and enfeeble his country. It might be a close run thing, but in this instance Russia has more right on its side than the West".List of works
War and an Irish Town (1973)
War and Peace in Northern Ireland
Dear God – The Price of Religion in Ireland
He has also edited two books on Bloody Sunday:Bloody Sunday: What Really Happened (1992)
The Bloody Sunday Inquiry: The Families Speak Out (2005).
McCann was the partner of Mary Holland (1935–2004), a journalist who worked for The Observer and The Irish Times. He has a daughter from that relationship, Kitty, who is now a journalist for The Irish Times, and a son, Luke, who works for the US-based human rights think tank The Center for Economic and Social Rights (www.cesr.org). The academic and activist Goretti Horgan has been his partner since the mid-1980s and they have an adult daughter, Matty.
McCann is a supporter of Derry City Football Club. In the 2002 film Bloody Sunday, McCann was played by Irish actor Gerard Crossan.