Prior to starting his PhD candidature, he completed his national service as a research scientist for the Finnish Defence Forces.

Early works included his first published short story "Shibuya no Love"[3] in 2003 and his short story "Deus Ex Homine" in Nova Scotia, a 2005 anthology of Scottish science fiction and fantasy, which caught the attention of his current literary agent, John Jarrold.

[4][5] Rajaniemi gained attention in October 2008 when John Jarrold secured a three-book deal for him with Gollancz,[6] on the basis of only twenty-four double-spaced pages.

[11] A sequel, The Fractal Prince, was published in September 2012 by Gollancz in Britain, and in October 2012 by Tor in the U.S.[12] The third book in the series is called The Causal Angel, and was published in July 2014 by Gollancz in the U.K. and by Tor in the U.S.[13] Rajaniemi has stated that the literary works of Jules Verne originally inspired both his career in science, as well as his science-fiction writing.

[14] Other influences include Maurice Leblanc, Arthur Conan Doyle and architecture blogger Geoff Manaugh.