Thomas C. Blagrave's military career started as an Ensign in the 25th Bengal Native Infantry in 1836. He was subsequently promoted to Lieutenant (1837), Captain (1850), and Major (1858), retiring with the rank of Lieutenant-Colonel in 1861. During the eighteen-fifties he and others compiled several maps of districts in the Punjab region of northern India. The maps were issued by the surveyor-general of India: Map of the district of Jalandhar (1852), Map of the district of Hoshiyarpoor (1853), District Umritsur, Punjab proper, 1850-53 (1855), The Jalandhar Dooab, comprising the districts of Jalandhar, Hoshiyarpoor and Kangra, 1847-52 (1855), and District Lahore, Punjab proper, 1851-53 (1856).
During May to July 1860 Blagrave made a series of photographs of Cape ferns at Wynberg, some of fresh specimens, others of dried specimens in his own herbarium or that of Dr. C.W. Ludwig Pappe*. He must then have been at the Cape for some time. A folio of these photographs is housed in the library of the National Botanical Institute in Pretoria. Blagrave was still at the Cape in 1864. In a letter written in November of that year by the Colonial Botanist, John C. Brown*, to W.H. Harvey* in Dublin, he mentions having passed on a message from Harvey to "Colonel Blagrave" in connection with a presumed new fern species of the genus Hymenophyllum. Specimens of this fern had been collected by Blagrave and a Mr. Drossel in a kloof above Kirstenbosch. Harvey thanked Colonel Blagrave "for specimens of the Hymenophylla found about Table Mountain" in the preface to Volume 3 of the Flora Capensis (1865).