Penttinen studied at the Viipuri Church Music School and then at the Sibelius-Academy with teachers Leevi Madetoja, Selim Palmgren and Sulho Ranta earning a diploma in composition in 1943. He then studied conducting with Jussi Jalas and earned a second diploma in organ in 1947 with Elis Mårtenson. He gave his first composition concert 1n 1942. He was a concert organist and chamber music pianist as well as an accompanist from 1947 on. From 1963 to 1971 he was the director of the Kotka Regional Academy of Music.
His music style features expressive melodies, vibrant rhythms, a natural pianism and motivic and polyphonic thought. He is best-known for his “Concerto per organo ed orchestra Op. 13” (1943). In addition he has composed a suite for orchestra “Pilviä” [Clouds] (1937), a symphonic poem “Katukuva” [Street Scene] (1936), a piano trio (1939), organ works and solo songs.