After completing his education at the Royal Military Academy in Brussels, he entered the Belgian army, joining the Regiment of Grenadiers, in which he eventually rose to the rank of Major.

[1] As soon as he reached the rank of Lieutenant he volunteered for service in the Congo Free State of King Leopold II of Belgium, and in 1887 he went out for a first term.

The story of this war was narrated in detail by Sidney Langford Hinde, who took part in it, in his book The Fall of the Congo Arabs.

The principal achievements of the campaign were the capture in succession of the three Arab strongholds at Nyangwe, Kasongo and Kabambari.

For his services, Dhanis was awarded the title of baron, and in 1895 was made vice-governor of the Congo Free State.