Admiral Nizam joined the Bangladesh Navy in 1979. He was promoted to officer in 1981 and has had a long and successful career. Ahmed served at the Naval Headquarters as the Director of Personnel and as the Secretary to the Chief of Naval Staff. As a specialist, he also taught at TAS School and Bangladesh Naval Academy. Admiral Nizam was also Director of Operations at Bangladesh Coast Guard Headquarters. He was responsible for selecting officers for the Armed Forces while holding the position of Deputy President of ISSB.

Admiral Nizam was in charge of torpedo boats, minesweepers, gunboats and other patrol boats. He got the proud privilege of commanding all three ex-RN frigates. Later he commanded various bases, including the biggest area in the Bangladesh Navy at Chittagong. More than two years, he served as Area Commander and earned a commendation from the Chief of Naval Staff. Admiral Nizam also participated in a peacekeeping mission in Ivory Coast during a time of tense situation as a Military Observer.

Admiral Nizam joined as the Chairman of Chittagong Port Authority in February 2012. He has done a good job and is still working there. As Chairman of Chittagong Port Authority, he opened the first Inland Container Terminal in the country. This was important because it helped keep the port open during labor strikes. Admiral Nizam also worked hard to establish a new sea port in the south of the country.