Many of Sonnergaard's works draw upon his own childhood in Copenhagen and he is noted for his distinctive and unconventional mix of cynical realism and social-surrealism.

Two more volumes were published in this trilogy: Last Sunday in October (2000) and I am still afraid of Caspar Michael Petersen (2003) which focused on middle and upper class life.

[8][9] In 2009, he published his first novel, About The Atomic Bomb’s Influence on the Youth of Vilhelm Funk, about the way the nuclear threat of the cold war was a subconscious motivation for many people's lifestyle in the 1980s.

Sonnergaard also authored a play and wrote numerous articles, features, and op-eds in various newspapers and magazines, primarily Politiken.

Most of his stories are told from a male perspective and often feature a retrospective glance at Sonnergaard's own youth or a visit to a foreign country.