Fabian Månsson was born in a poor family in Hasslö, an island in the Blekinge archipelago.
When the Social Democratic Party was split in 1917, Månsson who always opposed centralistic rule joined the radical, revolutionary group which formed the Social Democratic Left Party.
Fabian Månsson decided to rejoin the Social Democratic Party, but continued to scrutinize it from a radical angle.
His younger comrade Fredrik Ström wrote a biography about him, simply called Fabian (1948).
Today there is a statue of Fabian Månsson erected at his birthplace of Hasslö, and a bust outside Stockholm City Library.