Kosta Kolev graduated from the State Academy of Music in 1962. He studied Music Pedagogy, Conducting under Professor Georgi Dimitrov and Composition under Professor Parashkev Hadjiev. Since 1941 he played traditional music on accordion and made his name as one of the leading traditional music performers. In 1949 he began conducting a small traditional music orchestra. In 1951 he was appointed to conduct the choir and the traditional instruments orchestra at the Ensemble for Traditional Song and Dance at the Bulgarian National Radio.
He composed songs for traditional music choir and orchestra; pieces for solo instrument or voice accompanied by ensemble or orchestra; music to dance shows; suites based on traditional Bulgarian tunes, etc. He noted and arranged thousands of traditional songs and dances.
His works were recorded at the Bulgarian National Radio and the Bulgarian National Television and released on LP and CD. They were performed by The Mystery of Bulgarian Voices Ensemble as well as by traditional music ensembles in Veliko Tarnovo, Varna, and Ruse. His choral songs include Pushka pukna (A Gun Fired); Lepa Mara Sofianska (Beautiful Mara from Sofia); Ot med li ti sa ustata (What a Sweet Voice); and Izlel e Delio haidutin (Delio the Rebel Walked Out). His songs for choir and orchestra (1970 to 1980) include Lechko stapiay, Done (Step Lightly, Done); Galabi gukat (Pigeons Are Crowing); Maiden Denitza; Bone le (Bone, my girl); Oy, Nedo, Nedo; Jetva se zajena (Harvest time); and Prismehulka (A Tease). His orchestral works include Dances from Varna; Buenek; The Three Times; Balkan Rŭčenica; Sadovska Rŭčenica; Danec; Blatneška Kopanica; Petrič Dance. The lost flock (1974); Buenetzi (1979); Fantasy for solo pandore and orchestra (1973); and Safeta Loves Stoyan Kehaya for kaval and orchestra (1974). His suites include Harvest (1971); Rhodope (1972-73); Pirin (1973); Dobroudža (1975); Pazardjik for woman soloist, choir and orchestra (1976); Strandja; and Chirpan. His music to dance shows include Vintage Time (1978-79); Šop Fair (1976-77); Dobroudža Dances (1975-76); Varna Dance Suite (1974); and Thracians (1975).
Dances Kosta has taught include Kjustendilska Rŭčenica, Kulsko Horo, Novozagorsko Horo, Pravo Horo, Rŭčenica, Rŭčenica (from Dobrudža), and Tropanka.