A double majority is a voting system which requires a majority of votes according to two separate criteria. The mechanism is usually used to require strong support for any measure considered to be of great importance.

Two special cases that technically fit the definition but are usually not considered double majority are double chambers, where a law must have a majority in two chambers of a legislative body to pass; and quorums, where the measure requires not only a majority but also a turnout minimum.

In Australia, constitutional changes must be passed at a referendum in a majority of states (4 of the 6), and by a majority of voters nationally. Prior to 1977, the votes of citizens in the Northern Territory and the ACT did not affect the national or state-based count. After a Constitution Alteration put to referendum in 1977 and given vice-regal assent on 19 July 1977, Territorial votes contribute towards the national majority, but the Territories themselves do not count towards the majority of states. An earlier referendum in 1974, where the same proposed change had been bundled with a lowering of the required number of states to a half (3 of the 6) instead of a majority, had been defeated.

Since the patriation of the Canadian constitution in 1982, thorough amending formulae for the constitution were adopted. Per the Constitution Act, 1982, many amendments can be passed only by the Parliament of Canada and a two-thirds majority of the provincial legislatures, those provinces together representing at least 50% of the national population-–this is known as the 7/50 formula (as there were and are 10 provinces, so 7 constitutes a two-thirds majority). Additionally, a province can explicitly choose to dissent to an amendment that "derogates from the legislative powers, the proprietary rights or any other rights or privileges of the legislature or government of a province", in which case it does not apply in that province even if passed. Though not constitutionally mandated, a referendum is also considered to be necessary by some, especially following the precedent established by the Charlottetown Accord in 1992.

However, there are some parts of the constitution that can be modified only by a vote of all the provinces plus the Parliament of Canada; these include changes to the composition of the Supreme Court of Canada, changing the process for amending the constitution itself, or any act affecting the Canadian monarch or Governor General.

In the European Union, double majority voting replaced artificial voting weights for votes requiring a qualified majority in the Council of the European Union following implementation of the Treaty of Lisbon. A qualified majority requires 55% of voting EU member states, representing at least 65% of the population of voting members for a European Commission proposal to be approved. This increases to 72% of voting members states, representing at least 65% of the EU population of voting members should the proposal originate from a member state. Proposals can be blocked should a qualified majority of at least four Council members representing more than 35% of the EU population be formed.

Changing the constitution of Finland requires that a simple majority of the sitting Parliament vote in favor of the amendment. The amendment is postponed until the next general election. The next parliament may finally vote to ratify the amendment but by a two thirds of the MPs. Thus, a double majority of two different parliaments is usually required to pass constitutional amendments. An expedited process may however be entered if five sixths of the sitting parliament vote to declare an amendment urgent. Then, a two-thirds majority of the current parliament may ratify an amendment using the expedited process.

The elections to the French National Assembly are conducted in a two-round system. To avoid a runoff, the candidate must win a majority of the votes cast, which also has to be higher than 25% of the number of registered voters in their electoral district.