Her grandparents on her father's side were Protestant émigrés from Portugal, fleeing Catholicism and the authoritairian Estado Novo regime of António de Oliveira Salazar, arriving in Nouméa in 1952.

[2][circular reference] Her first job in Nouméa was at the government DTSI (direction des Technologies et Services de l'Information), while also teaching part time at the UNC.

She was suspended by Pierre Frogier in 2013, who said "your political line embodies all the conservatisms and all the archaisms by taking us back 25 years, far from the daring and innovative project that the Rassemblement carries today”.

[5][circular reference] Gaël Yanno and his supporters, including Sonia Backès, created the Caledonian Popular Movement (MPC, Mouvement populaire calédonien) which then won the elections, placing her in a strong position.

In the runup to a third referendum on independence from France (held in late 2021), she travelled to New York to address the United Nations on 17 June 2021, pleading unsuccessfully before the UN Special Committee on Decolonisation for the removal of New Caledonia from the list of non-self-governing territories arguing that “in New Caledonia, there is no longer an administering power and a colonised people.”[6] In July 2022, Backès, who had become a member of French President Macron’s Renaissance party, was appointed secretary of State for Citizenship in Prime minister Elisabeth Borne’s government.