From a Unitarian background, Praeger is raised in Holywood and attends the school of the Reverend McAlister and then the nearby Sullivan Upper School.
Praeger works in the National Library of Ireland in Dublin from 1893 to 1923. He co-founds and edits The Irish Naturalist, and writes papers on the flora and other aspects of the natural history of Ireland. He organises the Lambay Survey in 1905-06 and, from 1909 to 1915, the wider Clare Island Survey. He is an engineer by qualification, a librarian by profession and a naturalist by inclination.
Praeger is awarded the Veitch Memorial Medal of the Royal Horticultural Society in 1921. He becomes the first President of both An Taisce and the Irish Mountaineering Club in 1948, and serves as President of the Royal Irish Academy for 1931–34.
Praeger is instrumental in developing advanced methodologies in Irish botany by inviting Knud Jessen, the acclaimed Danish expert in Glacial and Post-Glacial flora, to undertake research and teaching in Ireland. This leads to the establishment of ‘paleoecology‘ as a distinct field of study in Ireland.
A vice-county system is adopted by Praeger dividing Ireland into forty vice-counties based on the counties. However, the boundaries between them does not always correspond to the administrative boundaries and there are doubts as to the correct interpretation of them.
(Pictured: Portrait of Robert Lloyd Praeger by Sarah Cecilia Harrison, National Museums Northern Ireland)