During her studies in psychology and pedagogy, Metz became involved in politics within the Luxembourg Socialist Party, via the Michel Welter Circle, which is mainly dedicated to health, education and disability issues.

In 2018, Metz succeeded Claude Turmes in the European Parliament, who had to leave his duties to replace Camille Gira, who died on 16 May 2018.

[4] She is also a permanent member of the Committee on the Environment, Public Health and Food Safety (ENVI),[5] and the Delegation for relations with South Africa (DZA).

Having participated in the drafting of the report "From Farm to Fork", she denounces the increasingly intensive agricultural policy oriented towards exports and the consequences of which are harmful to the environment.

[10] Concerning the Common Agricultural Policy (CAP), which represents almost a third of the European Union's budget, Metz regrets the lack of ambition and says that: "For the reform of the Common Agricultural Policy (2021-2027), I would have liked to see clear political objectives that would contribute to achieving the EU's climate objectives, to curb the disappearance of species and to encourage small farms rather than multinationals.

[22] Metz is involved in the cause of human rights, notably through her presidency of the Delegation for relations with the countries of Central America (DCAM)[23] in the European Parliament.

It informs itself and organizes work on the political, economic, social, legal and human rights situation in the nine partner countries of Belize, Costa Rica, Cuba, the Dominican Republic, El Salvador, Guatemala, Honduras, Nicaragua and Panama.

Metz believes that "for many citizens, the primary motivation in calling for stricter rules and more sanctions is an ethical concern, a desire to see animal suffering avoided or at least reduced.

She considers it a victory that the European Parliament voted in favor of an action plan to phase out the use of animals in scientific experiments and tests.

In February 2019, Metz demonstrated alongside two other MEPs from the Green Group (Molly Scott Cato and Michèle Rivasi); as well as other Belgian activists from the organization Agir pour la Paix at the military base of Kleine-Brogel (Belgium) by blocking the runway for F16s.