The movement, founded on September 1, 2021, was created by
Bill McKibben, a writer and
climate activist, who in the past had created the international climate organization
350.org. He created "Third Act" after turning 60 himself, to rally
baby boomers and the
Silent Generation to assist in the remaking of those systems that, according to the organization, now threaten future generations the most. In a span of 5 days, thousands of people had signed up to join the organization. In March 2023, the movement had gathered over 50,000 members, and participated in a protest in New York City using the slogan "Fossils Against Fossil Fuels", threatening to quit
Chase,
Citibank,
Wells Fargo and
Bank of America en-masse if they did not stop funding fossil fuel projects. In July 2024, the group organized a "die-in" in front of Citibank headquarters in New York City, resulting in the arrest of 46 of its members. The event also included ways to engage the wider public, such as
live music,
karaoke,
puppets and a
rocking chair brigade. The movement endorsed
Kamala Harris in the
2024 U.S Presidential elections, and its founder, Bill McKibben, kickstarted a fundraiser which accumulated up to $100,000 on July 25, 2024. During the "
All Out on Earth Day" protests which were held between April 18–30, 2025, they worked closely with the
Sunrise Movement,
Climate Power,
Popular Democracy,
Climate Defenders, the
Democratic National Committee Council on Environment and Climate,
Unitarian Universalists,
NAACP,
Dayenu,
Evergreen,
United to End Polluter Handouts Coalition,
Climate Hawks Vote, and the
Center of Biological Diversity (CBD). On 28 February 2025, the movement endorsed the "
Economic Blackout" protest, and gave directives on its official page, which included boycotting major retailers such as
Amazon,
Walmart and
Best Buy for non-essential purchases. On April 19, 2025 the movement organized a peaceful rally in
Farmington, Maine for the 250th anniversary of the
American Revolution, calling attention to threats against democracy and inaction on climate change alongside the
50501 movement. During the first half of 2025, Third Act began participating in
anti-Musk and anti-
Tesla demonstrations in the U.S. in protest of
DOGE's cuts in humanitarian aid,
dismantling of federal agencies and
mass firings of civil service employees. The movement is also participating in the
No Kings protests against
Donald Trump, co-operating with groups such as the
Indivisible movement,
50501, the
Nevada Labor Union,
Social Security Works,
Public Citizen and
Blue Band Alliance. As of June 2025, the movement claims to have over 70,000 members. In July 2025, the Third Act initiated an official partnership with the company
EnergySage. On September 21, 2025, the Third Act Movement joined the nationwide "Sun Day" celebration mobilization, promoting solar energy. During
Zohran Mamdani's campaign, the Third Act Movement openly supported him. On 18 October 2025, the Third Act Movement participated in the
No Kings Protest of October, stating itself as an active and willingful partner of the Indivisible movement, Public Citizen and Social Security Works in its organization. As early as in November 2025, the Third Act supported
Antonio Delgado for the
2026 New York gubernatioral election. The organization participated in organizing protests during the
Reneè Good protests and also told its members to contact their senators to state adversion to the increase of funds to DHS. == Ideology ==