Siward was a Danish follower of Canute and was rewarded with the title of Earl of Northumbria. In 1032 he also became Earl of Deira in 1032.

In 1054 Siward led a successful invasion of Scotland and after defeating Macbeth he replaced him as King of Scots with Malcolm Canmore.

Siward died in 1055 and was replaced by Tostig as Earl of Northumbria.