He was the youngest son of Birger Jarl,the de facto ruler of Sweden from 1250 to 1266, and Princess Ingeborg of Sweden, daughter of Eric X of Sweden. Older, non-contemporaneous Swedish literature has, for some reason, incorrectly stated that Benedict was the son of Birger"s second wife, Mechtild of Holstein, dowager Queen of Denmark.
However, Ingeborg died in 1254, the year of Benedict"s birth, at which time Mechtild, widow of Abel of Denmark, still lived in Denmark. Benedict pursued an ecclesiastical career. In 1284, some time after the death of his next-elder brother Eric of Småland, and during the reign of Magnus, Benedict was made Duke of Finland, the first known holder of that title and appanage.
The title may have been Duke of Sweden, the successor office to the position of Riksjarl of Sweden, held previously by Eric of Småland, and earlier by Magnus.
In 1286 he was elected Bishop of Linköping. Linköping"s chronicle of bishops from 1523 tells of him: "Scriptores rerum suecicarum medii ævi".
There exist at least two of his wills, from 1287 and 1289. He died from the plague.
