Anna was the son of Prince Eni, a brother of King Redwald of East Anglia. He  lived through the troubled times of the early 7th century, when King Penda of Mercia sought to expand his borders at the expense of his East Anglian neighbours. In AD 635, he made a push for control of Middle Anglia and crushed the forces of King Egric in battle. Along with the retired King Sigebert, Egric was killed in the fighting and Anna found himself taking on his brother's throne.

Anna had probably been converted to Christianity by St. Felix during his first visit to Sigebert's court in AD 631. Bede describes him as "an excellent man of royal descent" and he is generally supposed to have been extremely pious. He married twice - secondly to a lady named Saewara - and became the father of at least five saintly daughters, the Princesses Saethrith, Sexburga, Etheldreda, Withburga and Ethelburga. In AD 645, the lands of King Cenwalh of Wessex were also attacked by Penda of Mercia. Cenwalh found himself obliged to flee the kingdom and chose to find sanctuary with his fellow Christian monarch, Anna, in East Anglia. He stayed three years before it was safe to return. Around AD 650, however, it was Anna himself who was on the run, when Penda turned on East Anglia once more. Anna managed to rescue the monks from the Royal monastery at Burgh Castle, but was then forced to flee. Things must still have been unstable in Wessex, for he turned instead to Magonset which was probably still under Welsh control at this time. However, Penda followed him, conquered Magonset and installed his son, Merewalh, as the new monarch. Anna was probably back in his own kingdom within the year, but his position was considerably weakened and, three years later, he finally lost control of Middle Anglia to the Mercians.

Predictably, King Anna eventually died resisting another Mercian invasion, in AD 654. He was buried at Blythburgh and his brother and successor, Aethelhere founded a monastery at Iken dedicated to his memory. Anna is sometimes called a saint.