Captain Kosierb joined the CF on 1 August 1975 and graduated from RMC Kingston in May 1979 with a Bachelor degree in Mechanical Engineering. In October 1980 Captain Kosierb completed his Air Nav training and was posted to 409Voodoo All Wx Sqn in Comox. He was shortly reclassified to Transport Nav, and was subsequently posted to 436 Herc Sqn in 1981. Between 1981 and 1984 Captain Kosierb flew across Canada and round the world in the United States, South America, Europe, the Middle East, and was promoted to his actual rank. In 1984 Captain Kosierb reclassified as a Military Engineer. During his career as a Military Engineer, Captain Kosierb served in various places such as Calgary, CFB Chilliwack, 4 CER Germany, CFB Portage, and Iran. Captain Kosierb was posted to Ottawa in 1990 where he served subsequently with D Mil E in the mines and explosives section, with Land Reserve Modernization Project as a requirements officer, with Director General Infrastructure, with CLS / DLFR (Engineers), with Director General Strategic Planning as the Administrative Officer, and finally with CLS in the G1 section reviewing and providing analysis of Summary Investigations and Boards of Inquiry.

Capt Kosierb is married to Judy since 1992 and they have two grown up men, Nick and Jason.