Born in Gothenburg, the son of a railway engineer, Arosenius began studying art at the Valand Academy in 1896 where he became friends with the sculptor, Gerhard Henning. In 1898, he was admitted to the Royal Swedish Academy of Fine Arts, where he shared a studio with Henning. He disliked the traditional style of teaching there and switched to the counter establishment, Artists' Association School.
Between 1903 and 1905, Arosenius travelled, studied and worked in Europe spending extended periods of time in Munich, Paris and Normandy and leading a Bohemian lifestyle.
The majority of Arosenius' works are small scale watercolours often with a satirical theme and frequently meditating on questions of good and evil, life and death.
In 1903, Arosenius' daughter, Eva known as Lillan (Little one) was born; Arosenius was devoted to his daughter and her arrival caused him to give up his Bohemian habits for a more quiet family life; he married Lillan's mother, Ida (Eva) Adler in 1905 and created the children's book 'Kattresan' for Lillan. Arosenius' later works reflect this change in personal circumstances, becoming more intimate in tone. Arosenius died tragically early at the age of 31, a coughing fit resulted in a burst blood vessel and the blood choked him to death. Arosenius was a haemophiliac.
A major retrospective of Arosenius' work was held the year after his death. In 1978, his self-portrait was features in a series of postage stamps and there are streets named after the artist in both Stockholm and Gothenburg. Arosenius' works are well represented in Stockholm's Nationalmuseum and Gothenburg Art Museum.