Behr was born into a family of farmers in the district of Oljorro, Arusha, Tanzania, then still Tanganyika. After the nationalisation of white-owned farms during the implementation of President Julius Nyerere's Ujamaa Policy of African Socialism in 1964, the family emigrated to South Africa. Here the family defined themselves as Afrikaners, with the Behr children attending Afrikaans language schools and the conservative Dutch Reformed church.

After leaving the South African Defence Force, Behr attended Stellenbosch University in the Western-Cape Province of South Africa. It was during this period (1985–1989) that Behr's creative work was first published several poems appeared in the university's annual magazine, "Die Stellenbosse Student". While a student there, Behr became an agent for the South African apartheid government, which was committed to monitoring the activities of students on university campuses to prevent political insurrection.

Behr has also written short stories and essays. The short story "Die Boer en die Swaan" (The Boer and the Swan) appeared in Die Suid-Afrikaan, November 1993. "Cape Town, My Love" appeared in 2006 in Cape Town: A City Imagined, edited by Steven Watson (Penguin). Also in 2006, “Socrates, Miss Celie and Me” was published in Gesprek Sonder Grense: Johan Degenaar Word 80. In Spring 2007, the journal The Truth About the Fact published "People Like Us," which is an extract from a lecture Behr gave at Wilfrid Laurier University in Canada in 2003. "A Tale of Two Towers: Language, Terrorism and Another Moment in History.” During 2009 the short short-story "Boy" was published in the international anthology Between Men Two. This story is Behr's response to the short story "Girl" by Jamaica Kincaid. In Fifty Gay and Lesbian Books Everyone Must Read, Behr looks at the impact of Alice Walker's The Color Purple on his own political and psychological development. Behr's work has, to date, been published in ten languages.

Behr's first published novel, The Smell of Apples (1995), appeared first in Afrikaans in 1993 (as Die Reuk van Appels). The book garnered significant recognition in the form of the M-Net Award, one of South Africa's most prestigious literary prizes, as well as the Eugene Marais and the CNA Debut Literary Awards in South Africa, and the Betty Trask Award for the best first novel published in the United Kingdom in 1996. The novel was also short-listed for both the Steinbeck and Guardian Literary Awards. In 1997 the novel received the Art Seidenbaum Award from the Los Angeles Times.

The attention attracted by the success of this book compelled Behr to speak publicly about his spying. In 1996, at a Cape Town conference on Truth and Reconciliation, he used his podium as keynote speaker to discuss his history in the South African military and his campus spy status. In 2000, Behr's second novel, Embrace, was published. Its mixed reviews may reflect enduring anxieties regarding Behr's student political activities. Praised by Felice Picano in the Gay and Lesbian Review Worldwide for its epic quality, universal reach and insistence on complexity it was reviled in The Sunday Times by Tim Trengrove Jones as a "baggy Monster of overstated anxiety." Embrace was short-listed for The Sunday Times Award in South Africa and the Encore Award in the United Kingdom. At the end of 2009 Behr published his third novel Kings of the Water. Kate Saunders in The Times reviewed it as : "Superbly written, thoughtful and unflinching, this terrific novel explores the mentality of the Afrikaner male – with wonderfully poetic use of the Afrikaans language." Novelist Christopher Hope, reviewing for The Guardian (January 2010), noted the spirit of Chekov's "The Cherry Orchard" and called the novel "one of the most moving to come out of South Africa in many years."

Behr died on 27 November 2015 in Johannesburg after a suspected heart attack.