[1] Erik was born in early 1339 as the eldest son of King Magnus Eriksson (1316–1374) who ruled both Sweden and Norway.

The marriage aligned with Magnus's strategic interests, as Beatrix's dynastic claims could strengthen his position in the ongoing conflicts with Valdemar IV of Denmark.

Additionally, the union could also advance Magnus' ambitions in Estonia, which Valdemar had nominally ceded to Louis as compensation for Margrete's unpaid dowry.

Beatrix is believed to have been around the same age as Erik, and one of Saint Bridget's revelations indicates that the marriage took place while she was still a minor.

In 1357, a Swedish rebellion forced King Magnus to share the rule of Sweden with his son Erik, who was allowed domain over most of Scania and Finland.