Born in Hartenholm, Schleswig-Holstein in wartime Germany, Tiedemann left school as a teenager. At 21 he settled with family in Wisconsin, and was later drafted to train in the US army's Medical Training Unit in Texas during the Vietnam War. He completed a BA at University of Wisconsin–Milwaukee, followed by an MA and a PhD at SOAS University of London. After taking several part-time posts, Tiedemann spent twenty years teaching Modern History of China in SOAS's Department of History, including a sabbatical at the Ricci Institute, University of San Francisco. After his retirement, he maintained a post as Professorial Research Associate at SOAS and as Professor of Chinese History, Shandong University, Jinan.^[2][3]

His research mainly concerned the history of Christianity in China, with a particular focus on Shandong and the Boxer Rebellion. He also edited the second volume of the Handbook of Christianity in China,^[4] which totalled over a thousand pages; about half of the entries he wrote himself.^[5] Tiedemann was also a review editor of Journal of Peasant Studies.^[6]

A festschrift was published in honor of Tiedemann, edited by two of his former students, entitled The Church as Safe Haven (2018).^[7]

Tiedemann died on 1 August 2019, after suffering from illness for many years.^{[3] [8]}

• Tiedemann, R. G. (2009). Reference Guide to Christian Missionary Societies in China: From the 16th to the 20th Century. Armonk, N.Y.: M.E. Sharpe. ISBN 9781315497310.
• Bickers, Robert; Tiedemann, R. G., eds. (2007). The Boxers, China and the World. Lanham, MD: Rowman & Littlefield. ISBN 9780742553958.
• Tiedemann, R. G., ed. (2010). Handbook of Christianity in China, Vol. Two: 1800-Present. Leiden: Brill. ISBN 978-9004114302.