He was the eldest surviving son of Sir William Cornwallis of Brome, Suffolk, and his second wife, Jane.

After his father's death, his mother married Sir Nathaniel Bacon.

After the wedding, in January 1631, King Charles I, Henrietta Maria and Susan Feilding, Countess of Denbigh wrote to congratulate his mother Jane, Lady Cornwallis Bacon, and ask her to forgive him for his disobedience and return him to her favour.

Samuel Pepys recorded his death in the famous Diary, and described him as a "bold, profane-talking man".

Another contemporary source described him as "a man of so cheerful a spirit that no sorrow came next his heart, and of so resolved a mind that no fear came into his thoughts".