Iain Maclean was born on 25 November 1902, son of Norman H. Maclean. He was educated at Cargilfield, then at the Royal Naval Colleges at Osborne [Isle of Wight] and Dartmouth [Devon]. In 1931 he married 1st, Evelyn Marjorie, daughter of R. A. and Mrs Winton Reid (having one step daughter); then 2nd, in 1973, he married Nancy Margaret, widow of E. A. Barnard.

Maclean joined the Navy as a cadet in 1916. During the Second World War he served in Combined Operations, and from 1941-43, was engineer officer of the battlecruiser HMS Renown. He was made a captain in 1945 and after the war commanded the stokers' training school at Torpoint in Cornwall. He also served at the Imperial Defence College in 1951 and on his promotion to Rear-Admiral in 1952 became Deputy Engineer-in-Chief of the Fleet, 1952-55. Maclean retired from the Navy in November 1955, taking on the position of Director of Marine Development for the Brush Group, 1956-60, also carrying out a research survey for the National Ports Council, 1963-64.

Maclean is primarily remembered as being the engineer officer who updated the Navy's propulsion technology and restored mobility to the Fleet. He had seen how far ahead the United States Navy was in its ability to stay at sea for long periods during the war, and in 1944 Maclean instigated a series of design studies which played a key role in enhancing the capabilities of the post-war Navy. Maclean was awarded the OBE in 1944, and the CB in 1954. He died on 17 April 1988.