An architect and urban planner who was born in Warsaw in 1907. He studied architecture at the Warsaw University of Technology where, among others, he was supervised by Marian Lalewicz and Stanisław Noakowski. He finished his studies in 1933. A year later, he received the first prize in the competition to design the District Court in Gdynia (together with Zbigniew Karpiński and Roman Sołtyński). Sieczkowski also designed the Polish Seamen’s Home and co-authored the development plan for the South Pier and the area around it. In 1935-1937, he worked for the Department of Area Development and Planning of the Government Office in Gdynia. After the war, he worked in Bristol in Great Britain, in Bulwayo in Southern Rhodesia (as an architect and later on the head of the area development and planning office) and in Salisbury (an architect and then the director of the Central Area Development and Planning Office). In 1967, he won the UN competition and became the adviser for area development and planning office in Malta. In the 70s, he returned to Great Britain and settled in Bath. He taught urban planning at the Gloucestershire Collage of Art and Design. Sieczkowski participated in the September Campaign and was awarded the Cross of Valour. He died in 1973 in Bath.