Japan Supreme Court Grand Bench to Rule on Same-Sex Marriage (2026)

On March 25, 2026, the Third Petty Bench of Japan's Supreme Court referred six lawsuits brought by same-sex couples against the national government to the Grand Bench. For the first time, Japan's Supreme Court is set to deliver a unified constitutional ruling on same-sex marriage.

The cases referred are from the "Marriage for All" litigation that has proceeded through the Sapporo, Tokyo, Nagoya, Osaka, and Fukuoka High Courts (plus a second Tokyo case). The plaintiffs argue that provisions of the Civil Code and Family Register Act that recognize only opposite-sex marriage violate Article 14 (equality under the law) and Article 24 (freedom of marriage) of the Constitution, and seek damages from the state.

At a press conference, Chief Justice Yukihiko Imasaki stated that the Court will "fairly hear both sides and render a just decision," signaling a careful review that weighs both legislative and public considerations.

A referral from a petty bench to the Grand Bench occurs when a significant constitutional judgment is required. Under Article 10 of the Court Act, the Grand Bench hears cases involving:

• A first-time determination — or a reversal of precedent — on whether a law, order, regulation, or disposition conforms to the Constitution
• A proposed departure from a previous Supreme Court interpretation of constitutional or legal provisions
• Other matters deemed appropriate for Grand Bench consideration

This referral reflects both the fundamental importance of the constitutional question to Japan's family law system and the split among the lower courts.

The Supreme Court is organized into a Grand Bench and three petty benches (First through Third). Ordinary appeals are heard by a petty bench of five justices, but particularly important cases are heard by all 15 justices sitting together as the Grand Bench.

The Grand Bench has convened only a few dozen times since World War II. Landmark decisions include:

• 1973 Parricide Aggravated Punishment Ruling: Article 200 of the Penal Code struck down as unconstitutional
• 2008 Nationality Act Ruling: Discrimination against children born out of wedlock found unconstitutional
• 2013 Inheritance Discrimination Ruling: Civil Code Article 900(4) proviso struck down
• 2015 / 2021 Same Surname Rule Rulings: Article 750 upheld (though with strong dissents)
• 2023 Gender Identity Disorder Special Case Act Ruling: Surgical sterilization requirement struck down

These rulings have all exerted significant influence on the Diet. A Grand Bench decision on same-sex marriage would be expected to create strong pressure for legislative reform of the Civil Code and Family Register Act.

"Marriage for All" lawsuits were filed simultaneously in five district courts (Sapporo, Tokyo, Nagoya, Osaka, Fukuoka) beginning in 2019, followed by second-wave cases. At the high court level, five courts ruled unconstitutional and one ruled constitutional — a 5-to-1 split that was a key factor in the Supreme Court's decision to convene the Grand Bench.

The five high courts that ruled against the current law generally reasoned as follows:

• Essence of the marriage system: Article 24(2) requires laws on marriage and family to be based on individual dignity and essential equality of the sexes. Completely excluding same-sex couples from marriage exceeds legislative discretion
• Violation of equality: Same-sex couples are entitled to equal legal protection, and different treatment based on sexual orientation violates Article 14(1)
• Legislative omission: Failure to provide any protective framework for same-sex couples constitutes a legislative omission exceeding the Diet's reasonable timeframe

The Tokyo High Court's second ruling upheld the current law for the following reasons:

• Legislative discretion: Designing marriage institutions falls within the Diet's broad discretion, and existing law cannot yet be deemed unconstitutional
• Room for gradual response: Legal protection can be built up gradually through mechanisms such as partnership ordinances short of full marriage
• Constitutional text: The phrase "consent of both sexes" in Article 24(1) was originally understood by the drafters as referring to opposite-sex unions

This split precisely creates the conditions requiring a unified Supreme Court ruling.

The Grand Bench's deliberations will focus on three main issues.

Whether restricting marriage to opposite-sex couples constitutes discrimination based on sexual orientation.

• Plaintiffs: Same-sex couples share essentially the same kind of relationship as opposite-sex couples yet are entirely excluded from marriage. This lacks a rational basis and is discriminatory
• Defendant (State): The marriage system is, by its very definition, premised on "one man, one woman." The issue is not about sexual orientation but about the definition of marriage itself

Whether Article 24(1)'s phrase "marriage shall be based only on the mutual consent of both sexes" includes same-sex marriage.

• Plaintiffs: While "both sexes" appears to reference opposite-sex couples, this reflects the drafting era only. A contemporary reading must center on individual dignity and freedom of marriage
• Defendant (State): Article 24(1) presupposes opposite-sex marriage, and excluding same-sex couples faithfully tracks the text

Interpretation of Article 24(2) — which places family law matters under the legislature — is also central. It requires legislation based on individual dignity and essential equality of the sexes, which several high courts cited as the basis for ruling unconstitutional.

Even if the current law has problems, are they within Diet discretion or beyond it?

• Plaintiffs: Although the 2015 Grand Bench upheld the same-surname rule, subsequent social changes mean that excluding same-sex couples from marriage today exceeds legislative discretion
• Defendant (State): The Diet has progressively responded through partnership ordinances and other measures. It would violate the separation of powers for the courts to force legislative reform of the marriage system itself

Grand Bench cases typically take one to two years. The anticipated timeline is:

1. During fiscal year 2026 (through March 2027): Oral arguments likely to be held, with cases consolidated
2. 2027 or later: Judgment
3. After the ruling: If unconstitutional, the Diet will likely begin amending the Civil Code and Family Register Act (even a finding of unconstitutional legislative omission does not require immediate amendment, but political pressure becomes overwhelming)

Historically, the Diet has moved to amend legislation within one to five years after Grand Bench rulings of unconstitutionality (such as the parricide and inheritance cases).

Japan currently has over 400 municipalities with partnership ordinances, but these confer only limited legal effect. Rights equivalent to marriage — inheritance, tax deductions, residence status, medical decision-making, adoption — are not recognized.

A Grand Bench ruling of unconstitutionality would bring expected changes including:

• Inheritance rights and survivor pensions
• Spousal tax deductions
• Recognition as "spouse" for residence status
• Clear medical decision-making authority
• Eligibility for special adoption

Municipalities already operating partnership schemes will need to review and potentially connect them to the marriage system. Those without partnerships will face pressure to develop comparable administrative services.

Many companies already extend benefits to same-sex partners (condolence leave, family allowances, company housing). Recognition of legal marriage would require additional adjustments:

• Revising the definition of "spouse" in work rules and policies
• Updating dependent tax deductions and social insurance procedures
• Treatment as accompanying family on overseas assignments
• Harmonization of HR systems in global companies

As of 2026, more than 40 countries and regions recognize same-sex marriage.

The U.S. Supreme Court in 2015 held in Obergefell v. Hodges that the Fourteenth Amendment's Due Process and Equal Protection Clauses guarantee same-sex couples the right to marry nationwide.

The Marriage (Same Sex Couples) Act 2013 legalized same-sex marriage in England and Wales, with Scotland (2014) and Northern Ireland (2020) following. Implementation came through parliamentary legislation rather than judicial decision.

Taiwan's Judicial Yuan (Constitutional Court) ruled in 2017 that restricting marriage to opposite-sex couples was unconstitutional, and the "Act for Implementation of J.Y. Interpretation No. 748" followed in 2019 — making Taiwan the first jurisdiction in Asia to recognize same-sex marriage. Taiwan's experience illustrates a collaborative model between the judiciary and legislature that could inform Japan.

Among the G7, Japan is the only country that recognizes neither same-sex marriage nor a national-level civil partnership. It is also in the minority among OECD countries. The Grand Bench ruling will test how Japan engages with these international currents.

The March 25, 2026, Grand Bench referral could mark a historic turning point in Japan's family law and human rights jurisprudence.

• The Third Petty Bench referred six same-sex marriage lawsuits to the Grand Bench
• The Grand Bench hears cases with all 15 justices and is reserved for constitutional rulings and precedent changes
• High court rulings have split 5-to-1 in favor of unconstitutionality, requiring a unified Supreme Court ruling
• Core issues involve Articles 14 (equality) and 24 (freedom of marriage), and the scope of legislative discretion
• Oral arguments are expected in fiscal year 2026, with judgment likely in 2027 or later
• A ruling of unconstitutionality would accelerate amendment of the Civil Code and Family Register Act
• With more than 40 countries — including the U.S., U.K., and Taiwan — already recognizing same-sex marriage, Japan's decision will draw international attention

The Grand Bench's ruling will send a powerful message to the Diet and will affect the legal status of same-sex couples, municipal partnership ordinances, and corporate HR systems across Japanese society. The next one to two years will be a pivotal period for reexamining the Japanese family.

If you have questions about legal protections for same-sex partners — wills, voluntary guardianship, asset management, adoption, and so on — please consult a family law attorney without delay. Even under current law, a significant amount of legal protection can be structured through private contracts and estate planning.