As a writer and speaker, Stewart has shown interest in controversies over religious freedom and the separation of church and state. She has also written about public and science education, public funding of faith-based initiatives, anti-LGBT initiatives on the state level, and bullying in schools in the U.S. Stewart began her journalism career working for investigative reporterWayne Barrett at The Village Voice. Since 2011, she has been an op-ed contributor to The New York Times, writing more than 15 columns. Her latest linked the slow federal response to the country's coronavirus outbreak to President Trump's connections to the far right and anti-science conservatives. Stewart also wrote almost 20 opinion pieces for The Guardian in 2012 and 2013, and began appearing there again in 2020. In addition, she has written for The American Prospect, George Washington University's History News Network, The Nation, Reuters, The Atlantic,Newsweek, Rolling Stone, The New York Observer, Santa Barbara Magazine, and Religion Dispatches. In 2012, after seeing that group's involvement in her children's public school, she wrote . Kirkus described it as "ompelling investigative journalism about an undercovered phenomenon." Alexander Heffner of the Minnesota Star Tribune wrote that the book "exposes the violation of church and state in schools", calling it "an important work" and "a fascinating exposé", and Stewart "a great digger for facts" and "a respectful narrator." In November 2016, Stewart wrote in The Nation, for which she had been writing since January 2015, about the role of Trump's shift on abortion as a factor in his 2016 election. She continued to write for the publication until June 2017. In March 2020, Stewart published The Power Worshippers: Inside the Dangerous Rise of Religious Nationalism, which outlines the decentralized Christian nationalist movement in the U.S. and its grabs for power, linking it to historical movements against abolition, the New Deal, and civil rights. The book was excerpted in the New York Review of Books and partially adapted in The New Republic. The Washington Post called it "required reading for anyone who wants to map the continuing erosion of our already fragile wall between church and state". Christianity Today charged Stewart with secular dogmatism, writing, "At times, her wariness toward white evangelicals and sense of conspiracy borders on the comical." She was interviewed on The Brian Lehrer Show, The Majority Report, and for Salon and Sojourners. In April 2020, she was quoted in a Rolling Stone article about Trump's ties to the Christian hard right.
