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Olga was born to Ernst and Mimmi (née Norlander) in 1917. She married Sven Dahl, who was a professor of geography at Gothenburg School of Business, Economics and Law before his death in 1979. Together they had four children: Östen, born in 1945; Gudrun, born in 1948; Ingolf, born in 1950; and Åslög, born in 1955.
Olga Dahl received her bachelor's degree in geography, law and economics from Lund University. In the early 1950s she worked as a freelance consumer issue journalist for the women's magazine Husmodern. After having moved to Gothenburg she began studying family history, and published a series of articles. In the late 1970s she wrote about the 1600s and 1700s in a book about Gothenburg, Göteborgs hjärta – en bok om människor, affärer och byggnader kring Kungsgatan (The Heart of Gothenburg - a book about people, things, and buildings around Kungsgatan), with several others, including Per Clemensson, who wrote about the period 1775-1875, and Sven Gulin, who stands as the editor.
On her 90th birthday she witnessed her crowning achievement with the public opening of a database, "Göteborgs tomtägare 1637-1807", which details around 900 properties in central Gothenburg and their owners over the two century period.
Olga was a member of the Gothenburg Regional genealogical society from the 1950s onward, and was a local writer for the Swedish Biographical Dictionary. She taught several hundred amateur researchers the basic skills of genealogy and also gave courses in local history.