André Marx studied German, linguistics and arts at the University of Osnabrück from 1994 to 1996. He then concentrated entirely on writing books.

Marx is a fan of the original U.S. stories of The Three Investigators and as such wrote his first The Three Investigators book, The sunken ship, in 1995 in his free time. Two years later, his first book, The Three Investigators – Poltergeist.

Between 1997 and 2007, he wrote 27 books of the German Youth Book Series The Three Investigators (Die drei ???), all of which were published as radio play. This included the two three-volume anniversary editions of the Toteninsel (100) and Firemoon (125). After announcing his temporary departure from the series in 2009, he returned in 2012 with the short story The Lost Cake, which was published in the short story volume The Mystery of the Seven, as the author of the series and has since written numerous books of The Three Investigators.