Hammer was a trained engineer and helped his father with the expansion of the Gällö sawmill.
He moved to Norway in 1899, where he worked as a Swedish Consul and as the French General Agent for the Narvik Iron Ore Line.
After the dissolution of the Swedish-Norwegian union in 1905, Hammer moved to Tromsø, and later to Christiania around 1911.
The same year, Hammer married Benedicte Jabobsen, who was born in 1891 in Tysfjord Municipality, Norway.
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