Mexico Senate election 2018 — Results

The vote in brief

The Senate election of 1 July 2018, concurrent with López Obrador's presidential victory, handed his Morena-led coalition an absolute majority of Mexico's upper house for the first time. The result completed the new president's command of Congress and ended an era in which the Senate, with its territorial basis, had acted as a brake on whichever party held the presidency.

How the voting works

The Senate has 128 members serving six-year terms, renewed in full at each general election. Ninety-six are elected by state: in each of the 32 federal entities the party list that comes first wins two seats and the runner-up list wins one (the "first minority" seat), guaranteeing the opposition representation everywhere. The remaining 32 are allocated nationally by proportional representation from a single closed list. This design deliberately tempers majorities, which made the size of the 2018 result all the more striking.

The campaign trail

The senatorial contest tracked the presidential race. Morena ran with the PT and PES as "Juntos Haremos Historia"; the PAN, PRD and Citizens' Movement formed "Por México al Frente"; and the PRI allied with the Green Party and New Alliance as "Todos por México". With López Obrador far ahead, the question was less who would win than whether his coalition could secure a Senate majority despite the chamber's built-in checks.

The results in detail

The Juntos Haremos Historia coalition won 69 of the 128 seats on 45.54% of the vote — an outright majority. The PAN-led Frente took 38 and the PRI-led Todos por México just 21, a humiliation for the party that had long dominated the states. Morena alone became the largest Senate bloc with 55 seats.

What followed

Control of the Senate let the new government pass ordinary legislation and confirm appointments at will, including the ratification of treaties such as the renegotiated USMCA trade agreement. But the coalition remained short of the two-thirds (86 seats) required for constitutional amendments and treaty-level changes, so the most far-reaching items of López Obrador's agenda still depended on winning over opposition senators — a constraint that persisted until the 2024 election nearly erased it.

How the chamber broke down

Within the victorious Juntos Haremos Historia coalition (69 seats), Morena itself won 55, the Labour Party (PT) 6 and the Social Encounter Party (PES) 8. The opposition Por México al Frente alliance took 38 — the National Action Party (PAN) 23, the Party of the Democratic Revolution (PRD) 8 and Citizens' Movement (MC) 7 — while the outgoing government's Todos por México managed just 21, of which the Institutional Revolutionary Party (PRI) held 14, the Green Party 6 and New Alliance 1. The PRI's fall from roughly 52 senators to 14 was the most dramatic single shift, and 2018 marked the first time a coalition built around a single presidential candidate, rather than the PRI, secured working majorities in both houses of Congress at once.

Compiled and reviewed from official results by ElectioMap. See our data methodology.