Short answer:
Gay marriage became legal across the entire United States on June 26, 2015 , when the Supreme Court decided Obergefell v. Hodges , requiring all states to license and recognize same‑sex marriages.

When did gay marriage become legal in the US?

The key date: June 26, 2015

  • On June 26, 2015 , the U.S. Supreme Court ruled in Obergefell v. Hodges that same‑sex couples have a constitutional right to marry.
  • This decision struck down state bans and made marriage equality the law in all 50 states and required states to recognize same‑sex marriages performed elsewhere.
  • The ruling rested on the Due Process and Equal Protection Clauses of the Fourteenth Amendment, treating marriage as a fundamental right that cannot be denied based on sex of the partners.

In simple terms: before 2015, some states allowed same‑sex marriage and others banned it; after Obergefell, every state had to allow it.

Before nationwide legalization

Even though the question is “when did gay marriage become legal in the US,” it helps to know there was a long build‑up.

  • Massachusetts was the first state to legalize same‑sex marriage on May 17, 2004 , after the Goodridge v. Department of Public Health decision.
  • Over the next decade, more states legalized same‑sex marriage through:
    • State court rulings
    • State legislatures
    • Voter initiatives and referendums
  • At the same time, many other states passed explicit bans on same‑sex marriage in statutes or constitutions, creating a patchwork of different rules across the country.

By early 2015, a majority of states already allowed same‑sex marriage, but couples in several states (including Ohio, Kentucky, Michigan, and Tennessee) were still barred from marrying or having their out‑of‑state marriages recognized.

The Obergefell v. Hodges case in a nutshell

  • Who: Same‑sex couples from several states in the Sixth Circuit (Ohio, Kentucky, Michigan, Tennessee) who challenged state bans on marrying or recognizing their marriages.
  • What they argued: That their state’s refusal to license or recognize same‑sex marriages violated the Fourteenth Amendment’s guarantees of liberty and equal protection.
  • What the Court held (5–4):
    1. States must license marriages between two people of the same sex.
    2. States must recognize same‑sex marriages lawfully performed in other states.

This is the moment most people refer to when they ask “when did gay marriage become legal in the US?” because it’s when nationwide marriage equality became reality.

What’s happened since then?

Even after nationwide legalization, LGBTQ+ rights have remained a live political and legal issue.

  • Advocacy groups have tracked hundreds of state-level bills in recent years that focus on areas like school curricula, pronoun usage, and gender‑affirming care, showing that cultural and legal battles continue even with marriage equality in place.
  • At the same time, same‑sex marriage is now recognized in dozens of countries worldwide , with the U.S. one of the earlier nations to establish it nationwide (it became the 17th country to do so).

Quick recap

  • Nationwide legalization date: June 26, 2015 – Supreme Court decision in Obergefell v. Hodges.
  • First U.S. state to legalize: Massachusetts , on May 17, 2004.
  • Why it matters: It guaranteed same‑sex couples the same legal marriage rights as different‑sex couples, no matter which state they live in.

TL;DR: If you’re asking “when did gay marriage become legal in the US” , the landmark nationwide answer is June 26, 2015.

Information gathered from public forums or data available on the internet and portrayed here.