During World War II, he saw active service in Italy and later served as a Monuments Man in Germany.

[1] Excavations as a student included the Roman villa in Rudston, and Hadrian's Wall under Eric Birley and Ian Richmond.

[4] In 1938, having completed his university education, Steer was appointed to the Royal Commission on the Ancient and Historical Monuments of Scotland as an assistant archaeologist.

[1] In the early part of World War II, he worked as a civil servant with the Scottish Office at St Andrew's House.

[2] Upon returning from Europe, Steer rejoined the Royal Commission on the Ancient and Historical Monuments of Scotland.

[4] He used his experience of using aerial photography for military intelligence, and applied it to his civilian career, discovering many unknown sites.

In the 1978 New Year Honours, he was appointed Commander of the Order of the British Empire (CBE) in recognition of his service as Secretary of the Royal Commission on the Ancient and Historical Monuments of Scotland.