[8] Her aunt was Elizabeth Keith, wife of George Gordon, 4th Earl of Huntly who would lead an unsuccessful rebellion against Mary, Queen of Scots in 1562.

Her first cousin was Lady Jean Gordon, the first wife of James Hepburn, Earl of Bothwell, who became the third husband of Mary, Queen of Scots.

At St. Giles Cathedral, Edinburgh or at Holyrood on 8 February 1561/2,[9] Agnes was married to James Stewart, the illegitimate half-brother and chief adviser of Mary, Queen of Scots, who had been created Earl of Mar the previous day.

[17] The last event was a supper in Cardinal Beaton's palace at the corner of the Cowgate and Blackfriar's Wynd, and afterwards the young men of the town came in procession, in "convoy" to greet her, some in masque costume in "merschance", a Scottish form of Mummery.

James later agreed to give up the title of Earl of Mar, it being an Erskine family perquisite, but retained the earldom of Moray.

[29] Elizabeth I sent a diplomat John Tamworth with money to fuel the quarrel, which was delivered to Agnes Keith at St Andrews.

She waiting on the coast of Fife, Scotland for eight days for Wilson, in vain, after his ship was captured by an English sailor Anthony Jenkinson, commander of the Aid.

[37] It was said that Agnes welcomed the English ambassador Francis Russell, 2nd Earl of Bedford, with a kiss, when he arrived at Stirling Castle for the baptism of James VI.

[38] In early February 1567, Agnes suffered a miscarriage,[39] which provided her husband with an excuse to hastily depart from Edinburgh; thus he was away when Lord Darnley was murdered.

In May 1568, before the Battle of Langside, she coldly informed her frightened cousin, George Gordon, 5th Earl of Huntly, "ye haf mad me angary".

She spent the two years following his assassination managing the family estates and fighting a series of legal battles in which she sought to obtain financial compensation for the time he acted as regent.

In Edinburgh Sir William Douglas helped Wood check the coffers containing Agnes Keith's clothes at Holyrood Palace.

[49] While Agnes was at Dunnotar, her mother-in-law, Margaret Erskine, looked after her second eldest daughter, Annabell at the New House of Lochleven Castle.

She told Agnes that "God sall send your Ladyschip barnis efter this, for ye ar young aneuch.

It was noted by Professor Jane E. A. Dawson of the University of Edinburgh that Annas (Agnes) and her husband had been journeying to Darnaway Castle in Moray where they had planned to spend the winter when news reached them of the 5th earl's death.

[56][57][44] Mary, Queen of Scots wrote to Agnes from Tutbury Castle soon after Moray's assassination on 28 March 1570 regarding these jewels.

[59] This was the "Great Harry", a diamond and ruby jewel given to Mary on the occasion of her first marriage by her father-in-law, King Henry II of France.

Agnes Keith wrote from Dunnotar on 2 November 1570 to William Cecil asking that he ensure Elizabeth I would help defend her and her children against Huntly's actions.

Agnes argued that she retained the jewels as a pledge for the debts owed to her for the expenses that the Earl of Moray had laid out as Regent of Scotland.

[66] She claimed that Moray's executors including William Douglas of Lochleven and John Wishart of Pitarrow, had not acknowledged these debts, and she could now provide details.

[67] When Agnes and her husband failed to hand over the jewels to the Privy Council, they were both "put to the horn" (declared rebels) on 3 February 1574.

Agnes canvassed the support of Henry Killigrew, an English diplomat in Edinburgh, sending him as a gift a "leische" of three hunting hounds.

[73] Agnes forwarded copies of letters and a series of offers or negotiation points between her and Morton to Francis Walsingham for consideration in September 1574, hoping for an English diplomatic response in her favour.

[77] Agnes sent the lawyer Thomas Craig to plead her case, on behalf of her daughters, for the money owed to Regent Moray, and losses incurred during Morton's pursuit of the jewels.

Agnes was attended in her illness by the physicians and surgeons Gilbert Primrose and John Craig and the apothecary Thomas Diksoun.

[85] It lists legacies and debts to several servants, including to her "gentlewoman servatrix", Marjory Gray, the Parson of Dollar, John Steill, and to Alexander Monteith, chamberlain of Campbell.

[87] Celebrated Flemish artist Hans Eworth painted portraits of Agnes and her first husband, the Earl of Moray in 1562 to commemorate their marriage.