Kosowsky was born in Tel-Aviv in 1949. He remained there after graduating from Renanium High School to study art at the Anvi Institute. Soon after, he went to Jerusalem to continue his studies at the Bezalel Art Academy. He worked as a set designer for television and cinema for several years before starting a teaching career in 1976 at the Anvi Institute and the Thelma Yellin Art School. From there, he again moved to Jerusalem in 1978 as a professor of art at the Bezalel Art Academy. Since 1983, he has been teaching at the Ramat-Hasharon Art Teachers Seminary. He took a year off in 1984 when he was awarded a fellowship at Cite Des Arts in Paris on a Ministry of Education Scholarship.
Avinoam continues to work to this day, with a grand selection of originals and serigraphs to his name. His colorful expressions and control of his medium exudes a care-free, yet disciplines style, where color and technique take his paintings beyond mere nude studies.