In 1491 and not later than 1494, she married Sir Richard Pole. On 28 November 1499 on the demise of her brother, Richard, Earl of Warwick, she became sole heiress not only of her father, George, Duke
of Clarence, but also of the Earls of Warwick and Earls of Salisbury. Her husband died about 15 November 1504, leaving her with five children.
In 1509 she became Lady of the Chamber to Queen Catherine of Aragon. Henry VIII gave her an annuity of a hundred pounds, and granted her and her heirs for ever the possessions of Richard, late 
Earl of Salisbury, her grandfather. When her brother's attainder was removed, she petitioned the King and, in 1513, was restored to the dignity of Countess of Salisbury.
On 21 February 1516, she took part in the christening of the Princess Mary at Greenwich and, from 1520 till after October 1533, was the Governess of the princess. In 1525 she accompanied the princess
into Wales. In 1533 Margaret was slightly implicated in the case of the revelations of Elizabeth Barton, the Nun of Kent. She returned to court and, in 1536, the king gave her lands in Yorkshire.
In 1538 Henry VIII persecuted her family on account of both their descent from Edward IV's brother, George, Duke of Clarence, and the action of her son, Cardinal Reginald Pole, who hoped that Pope Paul
III would publish a Bull of deprivation. Her youngest son, Sir Geoffrey Pole, was sent to the Tower, to be followed by her eldest son, Henry, Lord Montagu.
Information was then laid against her and she was examined at her house at Warblington by William FitzWilliam, Earl of Southampton, Lord High Admiral, and Thomas Goodrich, Bishop of Ely. She was then moved to the house of the Earl of Southampton at Cowdray, where she remained until she was transferred to the Tower of London.
On 12 May 1539 she was, without a trial, attainted by Act of Parliament, whereby all her honours were forfeited. On 28 May 1541 she was beheaded in the Tower. Chapuys, writing to Queen Mary of Hungary, spoke of her "very strange and lamentable execution," which took place "at the Tower in the presence of the Lord Mayor of London and about 150 persons more". In the absence of the executioner, "a wretched and blundering youth was chosen, who literally hacked her head and
shoulders to pieces in the most pitiful manner".
 

Source: Leo van de Pas