She was an activist before she became an atheist activist, once wanting to defect to the Soviet Union. But in 1960, she became an atheist activist when she sued the Baltimore school district for mandating official prayers and Bible readings, calling it unconstitutional. She and another activist with a similar case, Ed Schempp, sued all the way to the Supreme Court, winning in 1963. She later sued NASA for such things as the Apollo 8 astronauts reading the Bible, though she lost. She founded the activist group American Atheists in 1963, and she led it for the rest of her life.