Sider attended the University of Waterloo, in Ontario, and received a BA in European history. While at Waterloo, he came in contact with the apologetic work of InterVarsity Christian Fellowship, and set his sights on a career in academia. Upon graduating in the late 1960s with Master of Divinity and Ph.D. degrees in history from Yale University, he expected to teach early modern European history on secular university campuses, and continue his apologetic work for IVCF. In 1968, he accepted an invitation from Messiah College to teach at its newly opened Philadelphia Campus in the inner city of Philadelphia, PA. The racism, poverty, and evangelical indifference he observed at close hand made a deep impression that led him to write the book, Rich Christians in an Age of Hunger.
What he saw as the injustice of the inner city motivated Sider to work toward developing a biblical response to social injustice. He brought together a network of similarly concerned evangelicals, which in 1973 became the Thanksgiving Workshop on Evangelical Social Concern. It was this conference that issued the "Chicago Declaration of Evangelical Social Concern." Twenty years later, a similar gathering of evangelical leaders resulted in the Chicago Declaration II: A Call for Evangelical Renewal. In 2004 he was a signatory of the "Confessing Christ in a World of Violence" document.
He signed his name to a full-page ad in the 5 December 2008 New York Times that objected to violence and intimidation against religious institutions and believers in the wake of the passage of Proposition 8. The ad stated that "violence and intimidation are always wrong, whether the victims are believers, gay people, or anyone else." A dozen other religious and human rights activists from several different faiths also signed the ad, noting that they "differ on important moral and legal questions," including Proposition 8.
Sider has published over 30 books and has written over 100 articles in both religious and secular magazines on a variety of topics including the importance of caring for creation as part of biblical discipleship.
In 1977, Sider's Rich Christians in an Age of Hunger, was published. Hailed by Christianity Today as one of the one hundred most influential books in religion in the 20th century, it went on to sell over 400,000 copies in many languages. He later authored Good News Good Works, (published by Baker Book House), a call to the church to embrace what Sider sees as the whole gospel, through a combination of evangelism, social engagement and spiritual formation. Its companion book tells stories about effective ministries that bring both evangelism and social transformation together.
Completely Pro-Life, published in the mid-1980s, calls on Christians to take a consistent stand opposing abortion, capital punishment, nuclear weapons, hunger, and other conditions that Sider sees as anti-life. Cup of Water, Bread of Life was published in 1994. Living Like Jesus (1999) has been called Sider’s Mere Christianity. Just Generosity: A New Vision for Overcoming Poverty in America (1999, 2007) offers a holistic, comprehensive vision for dramatically reducing America's poverty. Churches That Make a Difference (2002) with Phil Olson and Heidi Rolland Unruh provides concrete help to local congregations seeking to combine evangelism and social ministry. Recent publications include: Fixing the Moral Deficit: A Balanced Way to Balance the Budget (2012); Just Politics: A Guide for Christian Engagement (2012); The Early Church on Killing: A Comprehensive Sourcebook on War, Abortion, and Capital Punishment (2012).
In August 2009, he signed a public statement encouraging all Christians to read, wrestle with, and respond to Caritas in Veritate, the social encyclical by Pope Benedict XVI. Later that year, he also gave his approval to the Manhattan Declaration, calling on evangelicals, Catholics and Orthodox not to comply with rules and laws permitting abortion, same-sex marriage and other matters that go against their religious consciences.
Sider's opponents typically criticize his ideas as consisting of bad theology and bad economics. The most thorough critiques come from the American Christian right, specifically from Christian Reconstructionists. David Chilton's book, Productive Christians in an Age of Guilt Manipulators (1986), with a foreword by Gary North, argues that Sider's book takes a position contrary to the biblical teachings on economics, poverty, and giving, and that the economic model it provides is untenable. Sider significantly revised the book for the twentieth anniversary edition, and, in an interview with Christianity Today magazine said, "I admit, though, that I didn't know a great deal of economics when I wrote the first edition of Rich Christians. In the meantime, I've learned considerably more, and I've changed some things as a result of that. For example, in the new, twentieth-anniversary edition, I say more explicitly that when the choice is democratic capitalism or communism, I favor the democratic political order and market economies."
Sider is the child of a Canadian Brethren in Christ pastor. He attends Oxford Circle Mennonite Church, is the father of three and lives in Lansdale, Pennsylvania with his wife Arbutus, a retired family counselor. They celebrated their 50th wedding anniversary in 2011, and they have six granddaughters. Sider's son Theodore (Ted) is a tenured professor of philosophy at Rutgers who has published over 50 scholarly articles and three books with Oxford University Press.