[2] She was notable for illegally entering the Y-12 National Security Complex in Oak Ridge, Tennessee, at the age of 82, with two fellow activists of the Transform Now Plowshares group.

The appeals court ruled that the prosecution failed to prove that Rice and the two others had the intention of causing injury to the national defense system.

[2][9] Frederick and Madeleine Rice were active participants in the Catholic Worker movement and considered Dorothy Day a good friend.

[14] Rice was arrested in the 1990s at protests against torture at the US Army School of the Americas[15][12] (now named Western Hemisphere Institute for Security Cooperation) at Fort Benning, Georgia.

August 2009, Megan Rice and Louie Vitale were arrested at Vandenberg Air Force Base protesting a test Minuteman III Intercontinental Ballistic missile (ICBM) launched approximately 4,000 miles to the Kwajalein Atoll in the Marshall Islands.

[20] Justifying their infiltration of the Oak Ridge facility, the trio cited both Biblical verses calling for world peace and the Treaty on the Non-Proliferation of Nuclear Weapons as justifications.

[22][21]The New York Times reported that nuclear weapons experts called this action "the biggest security breach in the history of the nation's atomic complex.

"[2] Rice, Walli, and Boertje-Obed were initially charged with misdemeanor trespass and "destruction and depredation" of government property (a felony)[2] and faced up to a $100,000 fine and up to a year in prison.

[30] On May 8, 2015, a 2–1 decision in the United States Court of Appeals for the Sixth Circuit found that the trio lacked the necessary intent for the sabotage conviction and overturned it for all three of them.