Dahlgren was born in Örebro to apothecary Rudolf Dahlgren and wife Greta née Dahlstrand. He took his MSc degree (1955) and PhD degree (1963) at Lund University. He continued working on South African plants during expeditions in 1956-57 and 1965–66, while affiliated with the Botanical Museum in Lund as docent. In 1973, he became professor of botany at the University of Copenhagen. Here, he developed his system of Angiosperm classification, based on many more characters simultaneously than previous systems, most notably many chemical plant traits. Although the system was first presented in Danish, it rapidly gained widespread acceptance, particularly due to the instructive diagrams, socalled Dahlgrenograms. His work on family circumscription in the Monocotyledons, published with H. T. Clifford and Peter Yeo, has had profound influence well into the molecular age. He was killed in a car crash in Scania, Sweden. A Rolf Dahlgren Memorial Symposium was held in Berlin, Germany later in 1987.
In 1986, he was elected member of Royal Swedish Academy of Sciences.
- Vem Är Vem - Skåne, Halland, Blekinge (ed. Åke Davidsson), 2nd edn. Bokförlaget Vem är vem, Stockholm, 1966; p. 167
- Dahlgren, Rolf (1963). Studies on Aspalathus and some related genera in South Africa (PhD thesis). Lund: Lund University.
- Dahlgren, Rolf (1974-76). Angiospermernes taxonomi, vol. 1-4. Copenhagen: Akademisk Forlag.
- Dahlgren, Rolf; Clifford, H. T. (1982). The monocotyledons: A comparative study. London and New York: Academic Press.
- Dahlgren, Rolf; Clifford, H. T.; Yeo, Peter (1985). The families of the monocotyledons: Structure, evolution, and taxonomy. Berlin and New York: Springer-Verlag.
- Strid, Arne (1987). "Rolf Dahlgren (1932-1987)". Taxon 36 (3): 698–699. JSTOR 1221891.
- "Author Query for 'R.Dahlgren'". International Plant Names Index.
- van der Merwe, J. J. M.; van Wyk, A. E.; Kok, P. D. F. (1988). "Dahlgrenodendron, a remarkable new genus of Lauraceae from Natal and Pondoland". South African Journal of Botany 54: 80–88.