The son of an Armenian entrepreneur and a Greek mother, he went to school at the St. George's Austrian High School in Istanbul and studied after his Abitur for some years in Vienna and in Stuttgart. Because of his father, he belonged to the Armenian minority for many years and did not have any citizenship; he became a Greek citizen shortly after 1974, together with the rest of the Armenian minority in Greece. Markaris speaks and writes in Greek, Turkish and German. Today he lives in Athens.

Before he began to write he studied national economy. Later he wrote several plays and cooperated with Theo Angelopoulos on a number of film scripts. He translated several German dramas into Greek such as Goethe's Faust I and Faust II, as well as Brecht's Mother Courage.

The Costas Haritos series of books (five novels and one collection of short stories, as of 2009) are very popular in several European countries such as Greece, Germany, Italy and Spain. Their main hero and first person narrator is a detective in the Athenian criminal police in his fifties, with a squabbling, fairly uneducated, and TV-addicted, but dearly loved wife, an aspiring, but stubborn, law student daughter, and an unpleasant, brown-nosing boss. It is hinted several times that Haritos assisted with the torture of leftist prisoners as a very young man under the Colonels' regime, a fact he is quite ashamed of now, and which makes him insecure whenever he has to deal with political leftists of all shades (obviously a fairly common species in Greece even today). Being somewhat old-fashioned (and not always too consistent) in his personal views, he deplores the loss of Greek traditions (but still has French croissant for breakfast rather than sesame rings), dislikes the masses of foreigners entering Greece (which doesn't stop him from befriending and highly respecting individual foreigners) and despises corruption (but gives large "tips" to his physician). His subjective self-deprecating comments contrast well with the objective high work-ethic and even heroism he displays. The modern Athens of rampant air pollution, ugly concrete buildings, constant traffic jams, and hordes of annoying tourists, is the backdrop of the first four novels (the fifth is set in Istanbul).

The first two books of the series have seen U.K. editions in English as well, under the titles (all straightforward translations from the Greek titles): "Late-Night News" ("Deadline in Athens" in the U.S.), and "Zone Defence"; the next two, "Che Committed Suicide" and "Basic Shareholder", are scheduled to be published in 2009 and 2010. The fifth novel in the series, not yet scheduled for publication in English, is called "Old, very Old".