Her photography helped to expose the human rights abuses in the Congo Free State under the regime of King Leopold II of the Belgians.

Alice gave her spare time to Frederick Brotherton Meyer's mission work at Regent's Park Chapel and later Christ Church, Lambeth.

Alice left the Civil Service to enter Doric Lodge, the training college of the Regions Beyond Missionary Union.

Four days later, as her honeymoon, Alice sailed with John on the SS Cameroon to the Congo Free State as missionaries with the Congo-Balolo Mission.

During her time in the Congo, Alice taught English to the local children, but her most important contribution was to photograph the injuries that were sustained by the Congolese natives at the hands of the agents and soldiers of King Leopold II of Belgium.

Leopold was partly exploiting the local population so fiercely to profit from increased rubber demand after the invention of the pneumatic or inflatable tyre by John Boyd Dunlop in Belfast in 1887.

In 1904, Alice's photographs reached wider distribution including Congo Slavery, a pamphlet prepared by Mrs. H. Grattan-Guinness, wife of the editor of Regions Beyond, and in King Leopold's rule in Africa[4] by E. D. Morel.

In December 1906, the daily paper New York American used Harris's photographs to illustrate articles on atrocities in the Congo for an entire week.

She continued her active speaking career and was listed with Christy's Lecture Service alongside Winston Churchill and Ernest Shackleton.