Early in May 1553, Jane was summoned to her parent's presence to be informed she was betrothed to Guildford Dudley, son of John Dudley, Duke of Northumberland. She protested, saying that she was already promised to Edward, Lord Hertford. This was probably the case, however it is unlikely that any formal arrangements had been made for Jane to marry Hertford. Jane may have made mention of this because of a dislike for Dudley and his family, not because of an affection for Hertford. Her parents assured her that her life would go on as before. Her studies would not be interrupted and she was to continue living with them at Suffolk Place.

On 25 May 1553 ( may have been 21 May* ) Jane was married to Guildford at Durham House on the Strand in London. In the same ceremony, Jane's sister, Lady Katherine, was married to Lord Herbert, son of the Earl of Pembroke, and Northumberland's daughter, Katherine, to Lord Hastings. Jane's younger sister, Lady Mary Grey, was betrothed to her cousin, Lord Arthur Grey. The marriages allied Northumberland to three of the most powerful families at Court.

The wedding was planned so hastily, that the wedding apparel had to borrowed from the Royal Wardrobe. Jane wore a headdress, 'of green velvet, set with precious stones. She wore a gown of cloth of gold and mantle of silver tissue. Her hair hung down her back, combed and plaited in a curious fashion.'

A feast followed the ceremony, after which the bridegrooms left to joust in the royal tiltyard at Whitehall.

June 1553
Ten days after the marriage, Northumberland divulged his plan to Jane's parents. In June, Jane was moved to Durham House where she and Guildford were to live as man and wife. Jane later wrote of the Duchess of Northumberland becoming 'enraged' against her when she protested at having to leave her family home. It was at this time that Jane was informed of Edward's illness and to hold herself in readiness for whatever he may wish for her. Jane wrote later that she thought the Duchess's words were little more than boasting, and bore little consequence.

Edward VI was growing weaker each day, and Northumberland knew he must hurry to complete the final stage of his plan. Vulnerable and delerious, Edward was easily convinced that he must strike his Catholic sister Mary from the line of succession if he was to be true to his father's name and in his duty to God. Edward's councillors were reticent. Any change to the succession required the consent of Parliament. If Northumberland failed in his scheme and Mary acsended the throne, they would be punished for their disloyalty. Northumberland, a skilled politician, met their hesitation with abuse. He put his case, 'with a great rage and fury, trembling for anger,' threatening to ' fight any man,' who defied him. A few councillors were later to report that they feared for their lives if they did not obey him.

Northumberland's plans culminated in the King's 'Device.' The document, signed by Edward's council, removed both Elizabeth and Mary from the line of succession, naming Frances Grey and her offspring as the heirs to his dominion. Frances Grey was summoned to the king's bedside where she formally asceded the throne to her daughter, Jane.

* Jane's biographers are divided over the exact date of the wedding, and both dates have been mentioned