He was born on 21 January 1863 (in 1860, according to some sources) in Warsaw; he completed a technical railway school and then, at the age of 15, he began working as a tunnel caretaker at the construction of the Dęblin-Dąbrowa Górnicza railway line. In 1885, he made his debut as an actor in the Sellin’s summer theatre in Łódź in a play entitled Żart sceniczny w jednej odsłonie. Later on, thanks to the help from Dionizy Henkiel, he published a novel entitled Janek, a short story Nasz mały and a volume of short stories Widmo. When another collection of short stories Druty telegraficzne appeared in 1889, Kosiakiewicz gave up his job at the railways, focusing on writing and starting regular cooperation with, among others, Gazeta Polska, Kurier Codzienny, Kurier Warszawski and Ateneum. In 1890–1893, he travelled around Europe, visiting England, France, Switzerland and Italy. At the same time, he continued his education, and, among others, attended lectures in medicine and sociology in Zurich as well as lectures in mathematics and philosophy at the Sorbonne in Paris. He stayed in Paris also in 1895–1897, working as a correspondent for Kraj, a journal published in St. Petersburg. After returning from Paris, he initially stayed in St. Petersburg, and then moved first to Warsaw and subsequently to Milanówek. In 1898, together with Ludwik Straszewicz, he founded Kurier Polski and collaborated with magazines such as A. Donimirski’s Słowo and S. Krzywoszewski’s Świat as well as the Galician press. Towards the end of 1905, he became a member of the Real Politics Party (Stronnictwo Polityki Realnej). Later on, he undertook translations, including works by William James and Cardinal Desiré-Joseph Mercier. In 1910, his five-volume tragedy Dzwonnik received an honourable mention during the Juliusz Słowacki competition. He died on 16 November 1918 in Warsaw.