[citation needed] Muñoz Ledo was Mexico's Permanent Representative to the United Nations from 1978 to 1985, where he presided over the UN Security Council, the Group of 77 and the negotiations of the Global Economic Agreements.

[citation needed] In 1988 he broke with the PRI and won a seat in the Senate running as a candidate for the leftist Frente Democrático Nacional (FDN) coalition.

On 5 May 1989, Muñoz Ledo, Cuauhtémoc Cárdenas, and other leading center-left and leftist politicians formally founded the Party of the Democratic Revolution (PRD).

[citation needed] In 2005 he returned to the PRD to join Andrés Manuel López Obrador in his presidential campaign.

[6] On 27 August 2018, the parliamentary group of the National Regeneration Movement (MORENA) proposed him as president of the Chamber of Deputies and therefore of the Congress of the Union for the first year of the LXIV Legislature.