The party was founded in 1934 following the left's defeat in the 1933 election, by the merger of Manuel Azaña's Republican Action, part of Marcelino Domingo's Independent Radical Socialist Republican Party and Santiago Casares Quiroga's Autonomous Galician Republican Organization (ORGA).

[2] Its members included José Giral, Victoria Kent, and Manuel Azaña, who became the party's leader.

Later, alongside the Republican Union, the party was the main component of the Largo Caballero government in September 1936, at the start of the Spanish Civil War.

The IR participated in all republican governments till the end of the civil war.

A party taking the name Republican Left was founded in 1977 and has achieved no major electoral success yet.