He started his railway career engineering parts of the London Underground in employment in London. When he took the job of Surveyor to the county of Cardiganshire, he also held the role of deputy engineer of the Manchester and Milford Railway, which never reached either of the locations in its title, being restricted to a line between Strata Florida and Pencader, Carmarthenshire. However, he became good friends with the line's manager James Cholmeley Russell, and resultantly later became civil engineer to the North Wales Narrow Gauge Railways and in 1906 became a director. Russell and Szlumper were two of the proposers of the Vale of Rheidol Light Railway from Aberystwyth to Devil's Bridge (originally proposed by the Manchester & Milford Railway), although Russell resigned from the VofR project in its infancy in 1899.