Marks attended the Garw Grammar School in Pontycymer, followed by Balliol College, Oxford between 1964 and 1967 to study Natural Science, Physics (B.A., Oxon). Among his friends at Balliol was the epidemiologist Julian Peto, and the journalist Lynn Barber . After this he studied Physics (Grad. Inst P.) at the University of London (1967 to 1968). Then, back to Balliol, Oxford (1968 to 1969) to study History and Philosophy of Science (Dip. H.Ph. Sc.) and then on to the University of Sussex (1969 to 1970) to study Philosophy of Science.

He spent seven years imprisoned in the Federal Correctional Complex, Terre Haute, Indiana. During his smuggling career, he claims not to have used violence and to have refused to deal with hard drugs. Both he and his now ex-wife Judy Marks were extradited from Majorca, Spain to Florida. They have three children together; Amber, Francesca and Patrick. He also has an older daughter, Myfanwy, from a 5 year relationship with Rosie Lewis.

Since his release from prison, Marks has published a best-selling autobiography, Mr Nice (Secker and Warburg, 1996), which has been translated into many languages. Along with 'Mr Nice', Howard has also compiled an anthology called The Howard Marks Book of Dope Stories (Vintage, 2001) and more recently a follow on from his autobiography; Señor Nice: Straight Life From Wales to South America. Marks is a campaigner for the legalisation of cannabis and tours the world with a one-man show. He also appeared in the documentary Stoned in Suburbia which aired on Sky1 in the UK. In October 2010, Howard hosted a documentary on Current TV titled 'Howard Marks On Drugs', which investigated drugs laws in the UK.

Judy Marks has also written her autobiography of their life together entitled "Mr Nice and Mrs Marks" published by Ebury Press, 2006.

Marks recorded the song 'Grow More Weed' with the UK dub punk band P.A.I.N.

Marks and long time friend Lee Harris recorded a song 'Three men in a boat' which was later remixed by River Styx and released on the album 'Angel Headed Hip Hop' on Genepool/Universal Ltd

Marks stood for election to UK Parliament in 1997, on the single issue of the legalization of cannabis. He contested four seats at once: Norwich South (against future Home Secretary Charles Clarke), Norwich North, Neath and Southampton Test. The average vote was over 1%. This led to the formation of the Legalise Cannabis Alliance (LCA) by Alun Buffry in 1999.

From 1999 to 2000 he was the honorary rector of Glasgow Caledonian University.

Marks had a role as a customs officer in the planned film Ecstasy, based on the bestselling book by Irvine Welsh and also made a cameo appearance in the 1999 film Human Traffic (in the "spliff politics" scene).

In 2010, he played a fictional role in the infamous gangster movie Killer Bitch.He is also the subject of a biopic starring Rhys Ifans as Marks entitled Mr Nice, named after his autobiography of the same name. Chloë Sevigny plays the role of his wife Judy. The film was released in October 2010.

• Official home page
• review of 'Mr. Nice'

Howard collaborates with British Artist KAV Kav Sandhu on The Track 'Mr Nice', part of 'The Mr Nice EP' due for release on October 18 2010 on This Feeling Records.