After graduating, Thomas subsequently embarked on his comedy career, initially supporting himself through working on building sites with his father.
Thomas' early exposure to comedy was through watching and listening to Dave Allen, Steptoe and Son, The Goon Show and Tony Hancock; his biggest influence was hearing a recording of Alexei Sayle: "It was like someone had kicked the door in - just listening to that tape and thinking that someone could do this stuff".
He also cited the playwright Trevor Griffiths as an early influence, describing him as "an absolute genius".
 He went on to write material for Dave Allen.

Prior to his most renowned vehicle, The Mark Thomas Comedy Product, Thomas was a frequent guest comic on the BBC Radio 1 show The Mary Whitehouse Experience, where he would do a routine about a specific topic of the week and involve studio audience members in the discussions.
He would also occasionally play parts in sketches written by the show's main performers.
He then became the resident stand-up comic on Saturday Zoo, a Channel 4 comedy series first screened in 1993 and appeared on an episode of Have I Got News for You.
He co-presented the highly successful Radio 1 comedy talk show Loose Talk with Kevin Day, and is a founder member of the London Comedy Store's hard hitting Cutting Edge show.

His political comedy show, The Mark Thomas Comedy Product (later renamed as simply The Mark Thomas Product, to reflect its increasing political agenda) on Channel 4 earned him criticism from politicians but was seen by critics as a crucial investigative tool.
In one edition, Thomas investigated the practice of avoiding inheritance tax by declaring art, furniture, homes and land available for public viewing.
After discovering that Conservative MP Nicholas Soames was claiming tax relief on a "three-tier mahogany buffet with partially reeded slender balustrade upright supports" on this basis, but without making any arrangements for the furniture to be inspected by the public, Thomas invented a 'National Soames Day' on which hundreds of people made appointments to see the furniture.
Soames subsequently decided to pay the tax on the item and Gordon Brown, then Chancellor of the Exchequer, changed the law.
In 2015, Thomas told The Independent's Adam Jacques: "I try to find the good in my enemies.
It's not unusual to be able to get on with people despite what they are doing being awful.
The only person I have met who I considered to be without any redeeming features was […] Nicholas Soames. […]
He was such a pantomime baddie."

Leaving Channel 4 was a mutual decision, following a series of disputes over how far the channel would go in its broadcasting, one of which concerned the channel's reluctance to support actions concerning corporate accountability and corporate manslaughter laws—a cause he had campaigned for—which coincided with the Queen Mother's funeral.
He declined to take part in a proposed Celebrity Guantanamo Bay 'reality TV' show.

Thomas has appeared at numerous comedy benefit nights, and is a well established stand-up comedian in the UK.
He is the chairman of the Ilısu Dam Campaign, a campaign which was successful in temporarily blocking the development of a large-scale hydroelectric dam in southeast Turkey that campaigners claim will lead to the displacement of up to 78,000 people, mostly Kurds, without adequate compensation or consultation, as well as to environmental and cultural destruction.

Recently, Thomas has been working with War on Want in India and investigating and filming alleged human rights violations in Colombia (by, amongst others, Coca-Cola) where trade unions are targeted by militia allegedly controlled by the government.

He wrote a regular column for the New Statesman between 2001 and 2007.

The parliamentary committee which oversees weapons exports, the House of Commons Quadripartite Select committee, commended him for his undercover work, which led to official warning letters being issued to a number of companies.

His work in this area is covered in As Used on the Famous Nelson Mandela: Undergro
After graduating, Thomas subsequently embarked on his comedy career, initially supporting himself through working on building sites with his father. Thomas' early exposure to comedy was through watching and listening to Dave Allen, Steptoe and Son, The Goon Show and Tony Hancock; his biggest influence was hearing a recording of Alexei Sayle: "It was like someone had kicked the door in - just listening to that tape and thinking that someone could do this stuff". He also cited the playwright Trevor Griffiths as an early influence, describing him as "an absolute genius".  He went on to write material for Dave Allen.
Prior to his most renowned vehicle, The Mark Thomas Comedy Product, Thomas was a frequent guest comic on the BBC Radio 1 show The Mary Whitehouse Experience, where he would do a routine about a specific topic of the week and involve studio audience members in the discussions. He would also occasionally play parts in sketches written by the show's main performers. He then became the resident stand-up comic on Saturday Zoo, a Channel 4 comedy series first screened in 1993 and appeared on an episode of Have I Got News for You. He co-presented the highly successful Radio 1 comedy talk show Loose Talk with Kevin Day, and is a founder member of the London Comedy Store's hard hitting Cutting Edge show.
His political comedy show, The Mark Thomas Comedy Product (later renamed as simply The Mark Thomas Product, to reflect its increasing political agenda) on Channel 4 earned him criticism from politicians but was seen by critics as a crucial investigative tool. In one edition, Thomas investigated the practice of avoiding inheritance tax by declaring art, furniture, homes and land available for public viewing. After discovering that Conservative MP Nicholas Soames was claiming tax relief on a "three-tier mahogany buffet with partially reeded slender balustrade upright supports" on this basis, but without making any arrangements for the furniture to be inspected by the public, Thomas invented a 'National Soames Day' on which hundreds of people made appointments to see the furniture. Soames subsequently decided to pay the tax on the item and Gordon Brown, then Chancellor of the Exchequer, changed the law. In 2015, Thomas told The Independent's Adam Jacques: "I try to find the good in my enemies. It's not unusual to be able to get on with people despite what they are doing being awful. The only person I have met who I considered to be without any redeeming features was […] Nicholas Soames. […] He was such a pantomime baddie."
Leaving Channel 4 was a mutual decision, following a series of disputes over how far the channel would go in its broadcasting, one of which concerned the channel's reluctance to support actions concerning corporate accountability and corporate manslaughter laws—a cause he had campaigned for—which coincided with the Queen Mother's funeral. He declined to take part in a proposed Celebrity Guantanamo Bay 'reality TV' show.
Thomas has appeared at numerous comedy benefit nights, and is a well established stand-up comedian in the UK. He is the chairman of the Ilısu Dam Campaign, a campaign which was successful in temporarily blocking the development of a large-scale hydroelectric dam in southeast Turkey that campaigners claim will lead to the displacement of up to 78,000 people, mostly Kurds, without adequate compensation or consultation, as well as to environmental and cultural destruction.
Recently, Thomas has been working with War on Want in India and investigating and filming alleged human rights violations in Colombia (by, amongst others, Coca-Cola) where trade unions are targeted by militia allegedly controlled by the government.
He wrote a regular column for the New Statesman between 2001 and 2007.
The parliamentary committee which oversees weapons exports, the House of Commons Quadripartite Select committee, commended him for his undercover work, which led to official warning letters being issued to a number of companies.
His work in this area is covered in As Used on the Famous Nelson Mandela: Undergro
Mark Thomas