Sighere was the joint king of the Kingdom of Essex along with his cousin Sæbbi from 663 or 664 until about 688.
While Sighere returned to paganism, Sæbbi remained Christian.
As a result of their rivalry, King Wulfhere of Mercia established himself as overlord of Essex, and induced Sighere to marry Wulfhere's niece Osgyth, daughter of Frithuwold, sub-king of Mercia in Surrey.
Jaruman, the bishop of Mercia, was assigned to reconvert the people of Essex to Christianity.
In 673, Sighere separated from Osgyth, who then fled to the protection of Bishop Beaduwine of North Elmham.