Steinunn Sveinsdóttir (1767–1805), was one of the most well known murderers in the history of Iceland alongside Bjarni Bjarnason (1761-1805).
In 1802, Steinunn Sveinsdóttir and Bjarni Bjarnason mutually murdered their respective spouses in Sjöundá in Iceland.
They were both arrested, subjected to torture and sentenced to death.
Steinunn Sveinsdóttir died in prison before she could be taken to Norway, but Bjarni Bjarnason was shipped to Norway, where he was executed in 1805.
The case has been the subject of two plays and a novel by Gunnar Gunnarsson, Svartfugl (1938).