Although he was ahead in the polls for both the first and second round of voting, which would have made him the first president of a Regional Council affiliated with the National Rally, he placed second in the election's second round, losing to incumbent Renaud Muselier, caused by a low turnout rate induced by the Covid-19 pandemic and an election delay.

[5][6][7] He was elected to the General Council of Vaucluse for the canton of Valréas from 1988 to 2001 and served as one of its vice presidents for the last nine years of his tenure.

[5][8] On 14 November 2010, he was appointed Secretary of State at the Ministry of Ecology, Sustainable development, Transport and Housing.

In April 2011, the Union for a Popular Movement selected Mariani as its candidate in the newly created eleventh constituency for French residents overseas (covering French citizens resident in most of Asia, the whole of Oceania, as well as part of Eastern Europe) for the 2012 legislative election.

Some commentators deemed the election to be the National Rally's best chance to win a regional majority for the first time in its history.

Mariani figures prominently as a friend of the Aliyev regime in the French documentary series by France 2, called Cash Investigation: Mon président est en voyage d’affaires.

Mariani has personal relations with the Aliyev family; he has repeatedly spoken alongside Mehriban Aliyeva, Azerbaijan's First Lady, at several Azerbaijani-organised events in France.

[16] Mariani is the Chairman of the NGO L'Eurasie, les nouveaux horizons, a member-organisation of the European Academy for Election Observation, an election observation NGO founded by Azerbaijan apologists Stef Goris and Alain Destexhe, which has promoted Azerbaijani interests in Europe.

[18] In July 2015, Mariani, accompanied by Russian officials, made a trip to Crimea which was annexed by Russia in 2014.

In interviews and meetings he expressed support: "We welcome the courage of the Crimean Parliament because it was able to make this decision despite the difficult situation and a great risk of escalation".

[19] In 2016, he brought non-binding resolutions to the National Assembly and Senate calling on the European Union to lift economic sanctions against Russia.

He is suspected of corruption, breach of trust and money laundering as well as influence peddling, since benefits, suspicious financial transactions and travels could have been possible compensation for positions favorable to the Kremlin.

[25] Researcher Marie Peltier presented him as an "agent of Damascus" for his role in the propagation of disinformation, particularly after chemical attacks, and in the dissemination of regime propaganda.

[26] In 2020, he called, in a plenary session at the European Parliament, to support the Assad regime to bring peace to the country, and to "exterminate the Syrian rebels".