[2] He studied road engineering in Lyon, and urbanism at Sciences Po in Paris as well as international cooperation at the University of the Basque Country.

[4][6] He also promoted the "Platform for Decent Housing" as well as became a member of Desazkundea, a group advocating for degrowth positions.

[3] One of the members of the foundational committee that created Equo in 2011, in March 2014 Marcellesi won the party primaries intended to determine the leading candidate for the upcoming May 2014 European Parliament election in Spain.

He became a member of the European Parliament on 11 October 2016, following the early renouncement of Sebastià (already agreed as part of the 2014 coalition deal between Compromís and Equo).

[8] Integrated within the Greens–European Free Alliance political group (Greens/EFA), Marcellesi served as member of the Committee on Agriculture and Rural Development, the Committee on Women's Rights and Gender Equality, the Delegation for relations with the Maghreb countries and the Arab Maghreb Union, and the Delegation to the Parliamentary Assembly of the Union for the Mediterranean.