[a] Ten political parties were allowed by the Supreme Electoral Court (TSE) to participate in the election.

The election resulted in a landslide victory for Nuevas Ideas, which won a majority of the legislative seats, mayors and municipal councils and PARLACEN deputies.

ARENA formed a coalition government with the National Coalition Party (PCN); the two parties agreed that ARENA deputy Norman Quijano would serve as the president of the Legislative Assembly from 1 May 2018 to 1 December 2019 and that PCN deputy Mario Ponce would serve from 1 December 2019 to 1 May 2021.

The presidential candidates were: Carlos Calleja of ARENA, Hugo Martínez of the FMLN, Josué Alvarado of Vamos, and Nayib Bukele of the Grand Alliance for National Unity (GANA).

[11] Bukele was inaugurated on 1 June 2019, becoming the first president to not be a member of either ARENA or the FMLN since José Napoleón Duarte of the Christian Democratic Party (PDC) left office in 1989.

[13][14] Bukele required the Legislative Assembly's approval, but ARENA and the FMLN, the legislature's two largest parties, both opposed the Territorial Control Plan.

[15] On 6 February 2020, Bukele invoked article 167 of the country's constitution which ordered members of the Legislative Assembly to convene an extraordinary session.

[18] In April 2020, after a spike in homicides, Bukele ordered large-scale prison lockdowns and authorized the PNC to use lethal force against gang members.

The constitution of El Salvador mandated that the election would be "free, direct, equal and secret".

[35] The following tables list the results of opinion polls for the 2021 legislative elections conducted between September 2019 and February 2021 in reverse chronological order.