Princess Cuneburga was the eldest daughter of King Penda of Mercia. Her father was an inveterate heathen and a cruel and savage devastator of his rivals and neighbours. He had many children, all of whom became Christians during his lifetime. Some were eminent for their sanctity, or their marriages to saints, and all for their generous patronage of the clergy and strenuous exertions in the cause of evangelisation. Cuneburga is the only one in whose name churches have been dedicated.

When, in AD 651, King Penda was flexing his muscles in the north, King Oswiu of Northumbria found it politique to enter into a peace treaty with him, sealing it by the marriage of his eldest son, Alcfrith, a pious Christian prince, to Penda's daughter, Cuneburga. If she was not already a Christian, she became so on her marriage and kept her house with so much regard to prayer and religious observances that it was more like a monastery than a court. She assisted her husband in the conver­sion of her brother Peada, who married Alcfrith's sister, Alchflaeda, two years later. King Alcfrith and Queen Cuneburga seem to have had at least six children: King Osric of Northumbria, St. Cuneburga of Gloucester, St. Edburga of Gloucester, St. Weeda of Gloucester, St. Eva of Gloucester and the extraordinary baby St. Rumwold.

Alcfrith joined his father in opposing Penda in AD 655, in the great battle of Winwaed where the Mercian King fell, fighting in his eightieth year. The following year, Alcfrith began to reign in Deira under with his father’s overlordship. He was a religious man and a friend of the clergy. With Cuneburga’s encouragement, King Alcfrith built the monastery of Ripon and the smaller one of Stamford. St. Wilfrid lived at their court for three years and was there ordained priest. Cuneburga was present, with her husband, at the famous Conference of Whitby in AD 664 where they, of course, took the Latin side in the theological arguments. When her husband died or was forced into exile later the following year, Cuneburga left Northumbria for the safety of her brother King Wulfhere's Mercian kingdom. She became abbess at Castor, near Peterborough in Northamptonshire, of which she was probably the founder. At the time, it was called Cuneburgcaster in her honour. Her sisters, St. Cunethrith, St. Cuneswith, St. Edburga of Bicester and St. Weeda of Castor, who had taken the veil at a young age, joined her there as nuns. The last two also became abbesses. Cuneburga's signature fol­lowed that of her brother, the King, in his charter giving the abbey of Medshamstead (Peterborough Cathedral) to the Church.

Cuneburga died on 15th September AD 680 and was buried at Castor where she soon became revered as a saint. In the 11th century, her body was translated to Peterborough, with those of her sister, Cuneswitha, and their kins­woman, Tibba. They later moved again, to Thorney. Her feast day is celebrated on the 6th March, the day of her translation.