Onni Alcides Tarjanne was born on 5 September 1864 in Virrat, Tampere region. Tarjanne’s parents were assistant vicar Karl Gustaf Törnqvist and Karolina Gustafva Regina Törnqvist (née Schreck). Onni Tarjanne and his brother changed the family name Törnqvist to Tarjanne in 1906, as a part of the finnicisation movement. The surname comes from the lake Tarjanne in Tampere region.
Onni Tarjanne studied architecture at the Polytechnical Institute of Helsinki and received his diploma in 1885. He continued his studies in München and made study trips to Scandinavia and Central Europe. Tarjanne worked as a teacher throughout his career. He was a teacher at the Turku Technical School the years 1887–1889 and lecturer of construction at the Polytechnical Institute of Helsinki 1889–1908. The years 1908–1917 and 1921–1928 he was the professor of construction at the Helsinki University of Technology.
Onni Tarjanne died at the age of 81, on 23 May 1946.