[4] He then went to University of Cambridge to work on beech forest under Arthur Tansley and obtained a MS in 1919 (after interruption by military service 1916–1918).

From working with Tansley, Watt became part of an academic lineage descended from Thomas Henry Huxley and Charles Darwin.

He continued his research on southern English beech forest in vacations and obtained a PhD from the University of Cambridge in 1924.

[11] Watt published a long series of scientific papers in the New Phytologist under the collective heading "Contributions to the ecology of bracken" (1940–1971).

Watt was a posthumous co-author of the substantive account on bracken in the Biological Flora of the British Isles.