Brotherson has been deputy leader of Tāvini Huiraʻatira since 2017 under the leadership of former President of French Polynesia Oscar Temaru.

He supports French Polynesia peacefully gaining independence from France through a local referendum possibly to be held in the 2030s.

He was head of the Post and Telecommunications department from 2005 to 2008, then chief of staff to Vice President of French Polynesia Antony Géros from 2011 to 2013.

He unsuccessfully promoted a bill seeking lifetime disqualification from office for politicians convicted of corruption[14][15] and advocated for French Polynesian independence.

[19] Brotherson was re-elected to the French National Assembly in the 2022 legislative election with 61.3% of the second-round vote under the New Ecological and Social People's Union (NUPES) alliance.

[20] On 10 March 2023 Tāvini Huiraʻatira announced that Brotherson would be their candidate for the presidency following the 2023 French Polynesian legislative election.

Brotherson appointed Eliane Tevahitua as the first female Vice President of French Polynesia in history.

In interviews after his election, Brotherson stated his support for an independence referendum, but estimated the timetable could take up to 10–15 years.