Zacharias was born in Madras, India. Zacharias descended from a line of Hindu priests (of the Nambudiri Brahmin caste). Missionaries spoke to one of his ancestors about Christianity and thereafter the family was converted and the family name was changed from Nambudiri to Zacharias. Zacharias grew up in a nominal Anglican household, and he himself was an atheist until the age of 17, when he unsuccessfully tried to commit suicide by swallowing poison. While in the hospital, a local Christian worker brought him a Bible and instructed his mother to read to him out of John 14. Zacharias says that it was John 14:19 that touched him and caused him to commit his life to Christ.

He immigrated with his family to Canada in 1966, earning his undergraduate degree from Ontario Bible College in 1972 (now Tyndale University College & Seminary) and his M. Div. from Trinity International University.

In May 1972 Zacharias married Margaret ("Margie") Reynolds, whom he met at his church's youth group. They have three grown children, Sarah, Naomi and Nathan.

He was later ordained by the Christian and Missionary Alliance and commissioned as an international evangelist. He founded Ravi Zacharias International Ministries in 1984 to pursue his calling as a "classical evangelist in the arena of the intellectually resistant."

Zacharias was invited to spend the summer of 1971 in Vietnam, where he evangelized to the American soldiers, as well as to POWs and Viet Cong. After graduating from Ontario Bible College he began an itinerant ministry with the Christian and Missionary Alliance in Canada. In 1974 the C&MA sent him to Cambodia, where he preached only a short time before its fall to the Khmer Rouge. In 1977, after graduating from Trinity, Zacharias was commissioned to preach worldwide.

In 1983, Zacharias was invited to speak in Amsterdam at the Billy Graham Evangelistic Association's annual evangelists' conference. It was here that he first noticed a lack of ministry in the area of Christian apologetics. After Amsterdam, Zacharias spent the summer evangelizing in India, where he continued to see the need for apologetics ministry, both to lead people to Christ and to train Christian leaders. In August 1984 Ravi Zacharias International Ministries was founded in Toronto, Canada. Today its headquarters are located in Atlanta, Georgia, and has offices in Canada, England, India, Singapore, and the United Arab Emirates.

In 1989, shortly after the fall of the Berlin Wall, Zacharias was invited to speak in Moscow. While there he spoke to students at the Lenin Military Academy as well as political leaders at the Center for Geopolitical Strategy. This was the first of many evangelism opportunities towards the political world. Future events included an invitation to Bogota, Colombia in 1993, where he spoke to the judiciary committee on the importance of having a solid moral foundation.

Zacharias took a sabbatical in 1990 and spent part of that year as a visiting scholar at Cambridge University. There he heard lectures by men such as Stephen Hawking and studied under professors such as John Polkinghorne and Don Cupitt. He also wrote his first book, A Shattered Visage: The Real Face of Atheism.

In 1993 Zacharias was invited to speak at his first Veritas Forum at Harvard University, and later that year was one of the keynote speakers at Urbana. Zacharias continues to be a frequent guest at these forums, both giving lectures and answering students in question and answer sessions at academic institutions such as the University of Georgia, the University of Michigan, and Penn State.

Zacharias attracted media attention when in 2004 The Church of Jesus Christ of Latter-day Saints (LDS Church) opened its signature pulpit at the Salt Lake Tabernacle to an outside evangelist for the first time in over a century (the last being Dwight L. Moody in 1871). Zacharias delivered a sermon on "Who Is the Truth? Defending Jesus Christ as The Way, The Truth and The Life" to some 7,000 lay-persons and scholars from both LDS and Protestant camps in an initiatory move towards open dialog between the camps.

Some evangelicals criticized Zacharias' decision not to use this opportunity to directly address the "deep and foundational" differences between the historic Christian faith and that of the LDS church. He responded by asserting that Christians should not immediately condemn Mormonism's theological differences but "graciously build one step at a time in communicating our faith with clarity and conviction". He said this is just as effective as showing someone the faults of their faith.The speaking engagement was nearly sabotaged by a claim by event organizer Greg Johnson, president of Standing Together, that Zacharias had nothing to do with editing the book The Kingdom of the Cults and had only loaned his name to the latest edition. Johnson later apologized for his comment.

Zacharias is also a frequent keynote lecturer within the evangelical community at events such as the Future of Truth conference in 2004, the National Religious Broadcasters' Convention and Exposition in 2005, the National Conference on Christian Apologetics in 2006.

On successive nights in October 2007, he addressed first the students and faculty of Virginia Tech, then the community of Blacksburg, Virginia, on the topic of evil and suffering in the wake of the Virginia Tech massacre. In addition, Zacharias has represented the evangelical community at occasions such as the National Day of Prayer in Washington, DC, the Annual Prayer Breakfast at the United Nations, and the African Union Prayer Breakfast in Maputo, Mozambique, and was named honorary chairman of the 2008 National Day of Prayer task force.

Zacharias was also interviewed in Focus on the Family's Truth Project.

In November 2009, Zacharias signed an ecumenical statement known as the Manhattan Declaration calling on Evangelicals, Catholics and Orthodox to engage in civil disobedience with regard to laws which the declaration claims would force them to accept abortion, same-sex marriage or other matters that go against their religious consciences.

Zacharias states that a coherent worldview must be able to satisfactorily answer four questions: that of origin, meaning of life, morality, and destiny. He says that while every major religion makes exclusive claims about truth, the Christian faith is unique in its ability to answer all four of these questions. He routinely speaks on the coherency of the Christian worldview, saying that Christianity is capable of withstanding the toughest philosophical attacks. Zacharias asserts that the apologist must argue from three levels: the theoretical, to line up the logic of the argument; the arts, to illustrate; and "kitchen table talk", to conclude and apply.

In particular, Zacharias's own style of apologetic focuses predominantly on Christianity's answers to life's great existential questions, with logical and scientifically inclined defense of God. In some discussion Zacharias appropriates to scientific matters, he answers the question of human origin. He has voiced skepticism over what he believes to be inadequate empirical evidence in the fossil record for an honest endorsement of the theory of evolution. He also questions the claim that evolution is compatible with the second law of thermodynamics, quoting the two to be inconsistent and irreconcilable. This stems from the belief that the second law of thermodynamics dictates that all closed systems in the universe will, unless acted upon by some external influence, tend to disorder. This notion, says Zacharias, does not conform to the key tenets of evolution, which postulate a marked increase in the order of biological life.