He was described by his Manchester Guardian obituarist as "a fiery and determined prophet on colonial affairs, especially as he saw them in East Africa".

Leys, whose Christian Socialism informed his belief in racial equality,[2] became an outspoken critic of the way in which the arrival of white planters had impacted Africans.

[1] In 1920, he responded to the Black Horror on the Rhine campaign orchestrated by E. D. Morel against the French use of African Troops in the occupation of the Rhineland.

Whereas Morel had claimed that African troops were particularly prone to rape, Leys denied this—based on 17 years experience in tropical Africa—and further stated that such allegations constituted "one of the great sources of race hatred" and "should never be repeated by any honest man or honest newspaper".

In 1938, with Leonard Barnes and Julius Lewin, he founded a socialist journal, Empire, subsequently taken over by the Fabian Colonial Bureau.