Waddell traveled extensively in India throughout the 1890s (including Sikkim and areas on the borders of Nepal and Tibet) and wrote about the Tibetan Buddhist religious practices he observed there. Stationed with the British army in Darjeeling, Waddell learned the Tibetan language and even visited Tibet several times secretly, in disguise. He was the cultural consultant on the 1903–1904 British invasion of Tibet led by Colonel Sir Francis Edward Younghusband, and was considered alongside Sir Charles Bell as one of the foremost authorities on Tibet and Tibetan Buddhism. Waddell studied archaeology and ethnology in-between his military assignments across India and Tibet, and his exploits in the Himalayas were published in his highly successful book "Among the Himalayas" (1899). Various archaeological excavations were also carried out and supervised by Waddell across India, including Pataliputra, of which he did not receive recognition of discovery until long after his death, in 1982, by the government of Bengal. His discoveries at Pataliputra were published in an official report in 1892.