[4] Thomas was educated at Macaulay Church of England Primary School, Victoria Rise, Clapham until 1974, where his party trick was to recite the first verses of the four gospels from memory.

[3] In a 2016 interview, he stated that he became an atheist at the age of 12, and subsequently developed an interest in radical politics during his teenage years, including anarchism, Marxism and Trotskyism.

In one edition, Thomas investigated the practice of avoiding inheritance tax by declaring art, furniture, homes and land available for public viewing.

[13][14] In 2008, he was awarded an honorary doctorate by the University of Bradford, for services to peace and for his work as a comedian, political activist, presenter and investigative journalist, especially for his effective campaigning on the ethics of the arms trade.

[16] For his 'It's The Stupid Economy' UK tour in 2009, Thomas played 55 shows over 14 weeks between March and end July, and encouraged each audience to come up with their own policies (silly or serious) that would somehow make their lives better, forming a "People's Manifesto".

His touring show entitled "Walking The Wall" (2011) was shortlisted for the Amnesty International Freedom of Expression award[18] and his book Extreme Rambling recounted the story.

Thomas revealed in 2013 that he had discovered, through a Data Protection request, that he had been under police surveillance as a result of his investigative journalism for Channel 4 and the New Statesman and put on the domestic extremist database.

"[19] The following year, Thomas and five journalists and photographers who had also been under surveillance by the London Metropolitan Police Service's National Domestic Extremism and Disorder Intelligence Unit (NDEDIU)[20] began legal action against the force.

[42] In his 4 March 2002 New Statesman column,[43] Thomas placed a bounty on the head of US President George Bush to the value of £4,320[37] (his total earnings writing for the magazine to that point).

In February 2009 British entertainers David Baddiel, Bill Bailey, Morwenna Banks, Sanjeev Bhaskar, Jo Brand, Russell Brand, Rob Brydon, Jimmy Carr, Jack Dee, Omid Djalili, Sean Lock, Lee Mack, Alexei Sayle, Meera Syal, Mark Thomas said in an open letter printed in The Times newspaper of the Baháʼí leaders to be on trial in Iran: "In reality, their only "crime", which the current regime finds intolerable, is that they hold a religious belief that is different from the majority.... we register our solidarity with all those in Iran who are being persecuted for promoting the best development of society ...(and) with the governments, human rights organisations and people of goodwill throughout the world who have so far raised their voices calling for a fair trial, if not the complete release of the Baháʼí leaders in Iran.

"[44] Echoing the comments earlier in the month made by two hundred and sixty seven non-Baháʼí Iranian academics, writers, artists, journalists and activists from 21 countries including Iran who signed an open letter of apology posted to Iranian.com and stating they were "ashamed" and pledging their support in Baháʼís achieving the rights detailed in the Universal Declaration of Human Rights for the Baháʼís in Iran.

[46] In December 2019, along with 42 other leading cultural figures, Thomas signed a letter endorsing the Labour Party under Jeremy Corbyn's leadership in the 2019 general election.

The letter stated that "Labour's election manifesto under Jeremy Corbyn's leadership offers a transformative plan that prioritises the needs of people and the planet over private profit and the vested interests of a few.

[49][50] The collection relates to Thomas' work as both comedian and activist, and includes audio-visual recordings, props and documents from performances, research material and drafts of publications.