The Finnish mezzo-soprano and contralto, Raili Onerva Kostia, studied at the Conservatory of Lahti, and from 1954 to 1957 at the Sibelius Academy in Helsinki as a student of Antti Koskinen, where she obtained a singing diploma.
Raili Kostia made her debut in 1958 at the National Opera in Helsinki as Rosina in Barber of Seville and belonged to this opera house until 1959. In 1960-1962 she sang at the Opera House of Graz, in 1962-1964 at the Staatstheater of Hannover, since 1964 at the Deutsche Oper am Rhein Düsseldorf-Duisburg, in which she was a member until 1968. Then she came back to Finland, where she continued her stage as her concert career. She gave successful guest performances and concerts in Germany, especially in Munich, Hamburg and Berlin, Austria and the skandinavishen countries. She performed at the festival in Savonlinna in 1970-1971 as Margaret in the opera Juha by A. Merikanto. She performed the role of the opera singer Aino Acktén in the movie Luottamus (Trust) in 1976.
Highlights in her stage repertoire were Cherubino in Nozze di Figaro, Dorabella in Cosi fan tutte, Octavian in Rosenkavalier, the Composer in Ariadne auf Naxos, Azucena in Il Trovatore, Eboli in Don Carlos and Ulrica in Un Ballo in Maschera by Verdi.
Raili Kostia taught at the Sibelius Academy. She was married to the organist Matti Kostia.
Recordings: DGG's Zauberflöte, sacred music), BASF (Penthesilea by Othmar Schoeck), Da Camera (Lieder).