Mikko Kyösti Heiniö (born 18 May 1948) is a Finnish composer and musicologist.
Mikko Heiniö was born in 1948 in Tampere, and studied composition with Joonas Kokkonen and piano with Liisa Pohjola at the Sibelius Academy in Helsinki from 1971 to 1975, and then studied composition with Witold Szalonek in West Berlin from 1975 to 1977 while at the same time beginning studies in musicology at the University of Helsinki.
He earned a diploma in composition from the Sibelius Academy in 1977, and a doctorate in musicology in 1984 from the University of Helsinki, where he lectured between 1977 and 1985 (Murtomäki 2001).
Heiniö's compositions include nine piano concertos, three symphonies and numerous chamber works for various instrument combinations.
He has written four operas: the church opera Riddaren och draken (The Knight and the Dragon, 2000), Käärmeen hetki (The Hour of the Serpent), premièred in September 2006, and Eerik XIV (Erik XIV), premièred in November 2011, and Johanna (2018).