Mexico's bicameral Congress of the Union and its two chambers

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Mexico's bicameral Congress of the Union and its two chambers

Background

Mexico's official name is the United Mexican States (Estados Unidos Mexicanos). Its national legislature, the Congress of the Union, is bicameral. The lower chamber, the Chamber of Deputies, has 500 members: 300 deputies are elected by plurality in single-member districts and 200 deputies are elected by proportional representation, through a closed regional list system, in five multiple-member electoral districts of 40 members each. Deputies serve a term of 3 years. The upper chamber, the Senate of the Republic, has 128 members. Two senators are elected by plurality in each state, one additional senator per state is awarded to the first minority party, and the remaining 32 seats are allocated by a closed-list proportional representation system. Senators serve a term of 6 years. A Permanent Commission made up of senators and deputies functions when the Congress is in recess.

Members of the Chamber of Deputies: 500 Members of the Senate: 128 Deputies elected by plurality in single-member districts: 300 Deputies elected by proportional representation: 200

Why it matters for exams: Comparative-government questions regularly set another federation's two chambers against the Lok Sabha and the Rajya Sabha, and Mexico is the standard example of a legislature that fills both of its houses by a mixture of plurality voting and proportional representation.

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3 October 2026 Source: Political Database of the Americas, Georgetown University

In plain words

Bicameral Two-chamber legislature — A legislature divided into two separate chambers that both take part in making law.

Plurality First-past-the-post voting — The candidate with the most votes wins, even without an absolute majority.

Closed list Closed party list — Voters choose a party and the party's own ranking decides which of its candidates take the seats.