The by-election was called after the Constitutional Council invalidated the election of Napole Polutele, miscellaneous left candidate in the June 2017 legislative elections and member of the UDI, Agir and Independents group in the National Assembly, on 2 February 2018.

Sylvain Brial defeated outgoing deputy Polutele in the first round of the by-election on 15 April.

Polutele, one of four deputies elected in the first round of the legislative elections,[1] sponsored the candidacy of Emmanuel Macron in the presidential election and announced that he would sit with the presidential majority in the National Assembly;[2] he ultimately joined the Constructives group as a related member, having sat as a member of the Socialist group in the previous legislature.

[3] After the election, Sylvain Brial decided to appeal the result to the Constitutional Council, claiming to have discovered irregularities in electoral lists and proxy votes.

[7] After his defeat, Polutele filed an appeal with the constitutional council on 26 April.