Born in Grosseto on 12 January 1973, Marras graduated from the "Guglielmo Marconi" scientific high school and immediately began his political career, being elected as a municipal councilor in Roccastrada in 1992 with the Democratic Party of the Left.

[2] He ran for the office of President of the Province of Grosseto at the 2009 provincial elections, supported by a centre-left coalition, and won at the second round to the centre-right candidate Alessandro Antichi on 22 June.

From 2012 to 2014, he represented Italy at the Council of Europe for the Congress of Local and Regional Authorities.

[2] In the 2018 general election, Marras was a candidate in the uninominal constituency of Grosseto for the Chamber of Deputies, on behalf of the centre-left coalition under the Democratic Party, garnering 28% of the votes and losing to the centre-right candidate Mario Lolini.

[9] On 22 October, he was appointed assessor of economy and tourism in the regional government led by president Eugenio Giani.