[1] A nonviolent activist for fundamental rights and liberties, in 2017 he undertook civil disobedience to push the Italian Parliament to approve new rules allowing legal euthanasia in Italy.

Cappato breached the law by helping an Italian tetraplegic and blind man from Milan to reach a Switzerland clinic where assisted suicide was legal.

During an unauthorized rally in Brussels to protest against censorship, he was arrested outside Le Soir newspaper building and jailed for a few hours[2] In 1997 and 1998 he was appointed Transnational Radical Party representative at the United Nations in New York City, where he worked on the establishment of the International Criminal Court and on the anti-prohibitionist campaign.

[3] From February 1999 to July 2001 he was the Coordinator of the "Radical Committee for the liberal revolution of the United States of Europe", the first political movement in 2000 to hold online voting for the election of the leading bodies.

[9] During his mandate at the European Parliament, Cappato gains approval by the EP on his proposals for a public registry of the elected members to fight against absenteeism of the Italian MEPs.

In 2004, elected Secretary of the Luca Coscioni Association for Freedom of Scientific Research, he is one of the promoters of the referendum for the cancellation of the new law on assisted reproduction.

In September 2006, together with Marco Pannella, Cappato embraces the fight of the Italian Radical Activist Piergiorgio Welby, sick of dystrophia and co-president of the Luca Coscioni Association.

Welby asks the President of Italian Republic to grant him the constitutional right to self-determination by suspending the vital treatment keeping him artificially alive.

To support Welby's cause, Cappato starts a hunger strike lasting for 17 days,[10] gaining wide public opinion attention in Italy and worldwide.

On 1 May 2012 he goes to Maastricht, The Netherlands, to commit Civil Disobedience against a new law issued by the government of Limburg Province, denying non-residents the consumption of light drugs in coffee-shops.

To press the Parliament discuss the issue, in December 2015 he undertakes a disobedience action by helping Dominique Velati, a woman at a terminal stage for colon cancer, to obtain Euthanasia in Switzerland.

In late 2016, Fabiano Antoniani, aka Dj Fabo, paraplegic and blind after a car accident in 2014, asked Marco Cappato to help him to get assisted suicide in Switzerland.

On 24 October the Court decided to suspend the decision and to reconvene on 24 September 2019, request Parliament to intervene to adopt appropriate legislative protections corresponding to the principles and rights enshrined in Italy's Constitution.

[15] In 2016 Cappato, together with Mina Welby, widow of Piergiorgio, accomplished a second disobedience by helping Davide Trentini, a man affected by Sclerosis, to reach Switzerland and obtain assisted suicide.

On 9 November 2021, Marco Cappato presents the appeal for a global carbon pricing in front of the PETI Committee of the European Parliament.