Sonik was a substitute for the Committee on Civil Liberties, Justice and Home Affairs, a member of the delegation for relations with the Maghreb countries and the Arab Maghreb Union (including Libya) and a substitute for the delegation for relations with the Mashreq countries.

At first he organized aid for the underground structures of Solidarność and he studied at the Institut d'Études Politiques de Paris.

Following the flood of 1997 he embarked on a scheme to save the Kościuszko Mound in Kraków and managed to collect approximately 15 million zloty for its restoration.

In cooperation with his friends from the Students' Solidarity Committee he established the Maj77 Association which organises events propagating democracy, freedom of speech and human rights.

He is active in the Institute of Heritage aiming to establish the European Culture Festival, and which also supports and promotes traditional professions, artistic craft and protects landscapes.

He won the trust of councillors from Civic Platform and Law and Justice, and he became the head of the largest group in the local government where he was the chairman of the Environmental Protection and Water Management Committee.

His time at the Parliament is divided between three committees: and six interparliamentary delegations: In the course of his work he has become involved in many issues which are important for the functioning of the entire European Union.

He co-wrote numerous resolutions concerning the protection of human rights in countries such as Syria, Lebanon, Cuba and Belarus, the Republic of Moldova and particularly in Trans-Dniestr.

He defended the interests of Polish entrepreneurs in the course of legislative works on a directive concerning the definition, description, presentation and labelling of spirits.

According to a report prepared by the Wrocław University in June 2007 he is one of 10 most active members of the Polish delegation in the European Parliament.

In May 2023, he resigned from membership in the Civic Platform, after party leader Donald Tusk required all candidates for parliament to support liberalizing abortion laws.