Colin Colahan was born in 1897 at Woodend, Victoria. He began to study art in 1917 at the National Gallery School under Bernard Hall and Frederick McCubbin, but soon left to study under Max Meldrum, with whom he developed his distinctive style, based on Meldrum's theories of "tonal values".
In 1935 Colahan left Australia for Europe. He never returned. He worked in England for much of his career, and during the late 1930s he built a reputation in London as an excellent portrait painter. In 1941 he was recommended for the official war art scheme.
During the Second World War Colahan was commissioned in 1942 and again in 1944. He began his work in Britain, depicting the activities of the Royal Australian Air Force and Australian Forestry Units, and completing several portraits of service personnel. His ability to work quickly in the field allowed him to work directly in oil, instead of having to do sketches for paintings to be developed later in the studio. After the surrender of Germany, Colahan went to Europe to capture the changing conditions in the liberated areas. He traveled through Belgium, France and Germany, painting the celebrations of VE day, fleeing refugees, and the destruction he saw in Berlin.
Colahan remained in Britain after the Second World War, but later moved to Italy, where he continued to work as a painter and sculptor.