His father was a school headmaster and his mother, Inger Margrethe Gaarder, was a teacher and author of children's books.

He established the Sophie Prize in 1997, an international award bestowed on foundations and individuals concerned with the environment.

The focus of his concern is the plight of Palestinian refugees, and he has vehemently criticized the Israeli occupation of the West Bank.

In August 2006, Gaarder wrote a controversial op-ed titled "God's Chosen People" that was published in the largest daily newspaper in Norway, Aftenposten.

Gaarder described Judaism as "an archaic national and warlike religion", contrasting it with the Christian idea that the "Kingdom of God is compassion and forgiveness".