She was the fourth wife of Charles Brandon, 1st Duke of Suffolk, who acted as her legal guardian during his third marriage to Henry VIII's sister Mary.

An outspoken supporter of the English Reformation, she fled abroad to Wesel and later the Grand Duchy of Lithuania during the reign of the Catholic Queen Mary I, to avoid persecution.

It seems Katherine was named for the queen, but her mother's lifelong friendship with Catherine of Aragon did not prevent her daughter from becoming one of England's Marian exiles later in life.

[1] According to Goff, Katherine likely spent her early childhood at Parham, as her mother was in almost constant attendance on Henry VIII's Queen, Catherine of Aragon.

Her father held some thirty manors in Lincolnshire, and almost the same number in Norfolk and Suffolk, worth over £900 per annum,[6] and Katherine is said to have been 'one of the greatest heiresses of her generation'.

She was promised to the Duke's son, but he is only ten years old, & although it is not worth writing to your Majesty, the novelty of the case made me mention it'.Although Suffolk was forty-nine and Katherine only fourteen, the marriage was a financially successful one.

As such, he played an important role in quelling the Lincolnshire rebellion in 1536,[16] and built an imposing residence at Grimsthorpe,[6] which came into Katherine's possession at the death of Elizabeth de Vere, Dowager Countess of Oxford, widow of the 13th Earl.

The marriage brought Katherine into the extended royal family, because Henry VIII's will made his younger sister Mary Tudor's descendants the next heirs to the throne after his own children.

This progress later became notorious for the queen's alleged adulterous trysts with her kinsman, Thomas Culpeper, though the duke and duchess's home at Grimsthorpe Castle was "one of the very few places on the route ... where Catherine Howard had not misbehaved herself".

[19] Noted for her wit, sharp tongue, and devotion to learning, by the last years of Henry VIII's reign the Duchess of Suffolk was also an outspoken advocate of the English Reformation.

[23] But their friendship remained strong, and after Henry VIII's death in 1547, the Duchess helped fund the publication of one of Catherine Parr's books, The Lamentation of a Sinner.

[24] Years later, the Duchess also became the custodian of one of her Brandon step-granddaughters, Lady Mary Grey, when the latter was placed under house arrest after marrying without royal consent.

Four months afterwards, attempting to reconcile herself to this tragedy, Katherine wrote to Sir William Cecil that “truly I take this [God's] last (and to the first sight most sharp and bitter) punishment not for the least of his benefits, in as much as I have never been so well taught by any other before to know his power, his love, and mercy, my own wickedness, and that wretched state that without him I should endure here”.

Their persecution by Stephen Gardiner, the Bishop of Winchester and Lord Chancellor, and subsequent wanderings were recounted in Foxe's Book of Martyrs, in an account probably written by Richard Bertie himself for the 1570 edition.

[31] These included brooches, tablets or lockets, one depicting Jacob's Ladder, another a town with a castle, another, the story of the Samaritan woman, with a number of jewelled gold "billaments" for wearing on a French hood.