Mixed-member majoritarian representation (MMM) is type of a mixed electoral system (parallel voting) using winner-take-all and proportional methods to elect two different groups of members, where the disproportional results of the members elected by winner-take-all system are dominant over the members elected by the Proportional representation system. Mixed member majoritarian systems are therefore categorized under semi-proportional representation, and are usually contrasted with mixed-member proportional representation (MMP) which aims to provide proportional representation compensation ("top-up") seats.

The most common type of MMM system is the supplementary member (SM) system (a form of parallel voting), whereby representatives are voted into a chamber using at least two different systems independently of each other. Most commonly this combines first-past-the-post (single member plurality) voting (FPTP/SMP) with party-list proportional representation (list-PR). The system has been applied in the election of national parliaments as well as local governments in various places such as Taiwan, Lithuania, Russia and Kazakhstan. While FPTP with list-PR is the most common pairing in parallel systems, any other combination is effectively possible. Therefore, not all parallel voting systems are mixed-member majoritarian (and not all MMM systems are strictly parallel - non-compensatory), however as most of them used in practice are, the terms are sometimes used interchangeably.

More unusual types of mixed-member majoritarian system are used in Pakistan, Italy and Hungary, and a de facto MMM system is used in South Korea.

According to the academic typology of Massicotte & Blais (1999), mixed-member majoritarian systems can come in the following forms:

Mixed-member majoritarian systems generally allow smaller parties that cannot win individual elections in a winner-take-all system to secure some representation in the legislature; however, unlike in a proportional system, they will have a substantially smaller delegation than their share of the total vote. Some articles argued that MMM does not lead to the degree of political fragmentation found in party systems under forms of proportional representation with no electoral threshold. The two tiers interact through contamination effects to increase political fragmentation.

A criticism of adding a proportional component to winner-take-all electoral systems is that the largest parties are more likely to rely on the support of smaller ones in order to form a government, compared to a two-party system. However, smaller parties are still disadvantaged as the larger parties still predominate. In countries where there is one dominant party and a divided opposition, the proportional seats may be essential for allowing an effective opposition. Furthermore, the likelihood of no governing majority is dependent on many other factors, same as under first-past-the-post. In many democracies, coalition governments are not only the norm, but seen as desirable as the government is formed with wider (indirect) support of the electorate and via compromise between factions.

In parallel voting and other supplementary member systems, it is sometimes considered a negative, that there are two classes of representatives with one class beholden to their electorate seat, and the other concerned only with their party.

The major critique of MMM systems is that they have lower overall proportionality. Large parties can win very large majorities, disproportionate to their percentage vote. For example, in the 2014 Hungarian election, the Fidesz/KDNP grouping won 133 of 199 Parliamentary seats with 44.87% of the overall vote.