On account of her nearness to the English crown, Lady Margaret Douglas was brought up chiefly at the English court in close association with the Princess Mary, who remained her fast friend throughout life. 

She was high in Henry VIII.s favor, but was twice disgraced; first for an attachment to Lord Thomas Howard, who died in the Tower in 1537, and again in 1541 for a similar affair with Sir Charles Howard, brother of Queen Catherine Howard. In 1544 she married a Scottish exile, Matthew Stewart, 4th earl of Lennox (1516-1571), who was regent of Scotland in 1570157I. During Marys reign the countess of Lennox had rooms in Westminster Palace; but on Elizabeth's accession she removed to Yorkshire, where her home at Temple Newsam became a centre for Catholic intrigue. 

By a series of successful manoeuvers she married her son Henry Stewart, Lord Darnley, to Mary, Queen of Scots. In 1566 she was sent to the Tower, but after the murder of Darnley in 1567 she was released. She was at first loud in her denunciations of Mary, but was eventually reconciled with her daughter-in-law. 

In 1574 she again aroused Elizabeths anger by the marriage of her son Charles, earl of Lennox, with Elizabeth Cavendish, daughter of the earl of Shrewsbury. She was sent to the Tower with Lady Shrewsbury, and was only pardoned after her sons death in 1577. Her diplomacy largely contributed to the future succession of her grandson James to the English throne. She died on the 7th of March 1578.

The famous Lennox jewel, made for Lady Lennox as a memento of her husband, was bought by Queen Victoria in 1842.

She was buried at the expense of Elizabeth I, in the same grave as her son Charles in the south aisle of Henry VII's chapel in Wesrminster Abbey. Her grandson James VI of Scotland (who later became James I of England) is said to have erected the fine monument (the monument to Mary Queen of Scots was later erected to the east of Margaret's). Her recumbent effigy, made of alabaster, wears a French cap and ruff with a red fur-lined cloak, over a dress of blue and gold. On either side of the tomb chest are weepers (small kneeling statues) of her four sons (two died young) and four daughters (all died young). The inscription panels read:

"HEER LYETH THE NOBLE LADY MARGARET, COUNTESSE OF LEVENOX, DAUGHTER AND SOLE HEIRE OF ARCHIBALD EARLE OF ANGUISE [Angus], BY MARGARET Q.OF SCOTTES HIS WIFE THAT WAS ELDEST DAUGHTER TO KING HENRY THE 7, WHOE BARE UNTO MATHEW EARLE OF LEVENOX HER HUSBAND 4 SONNES AND 4 DAUGHTERS. THIS LADY HAD TO HER GREAT GRANDFATHER K.EDWARD THE 4, TO HER GRANDFATHER K.HENRY THE 7, TO HER UNCLE K.HENRY THE 8, TO HER COUSIN GERMANE K.EDWARD THE 6, TO HER BROTHER K.JAMES OF SCOTLAND THE V, TO HER SONNE KING HENRY THE FIRST [ie.Lord Darnley], TO HER GRANDCHILD K.JAMES THE 6. HAVINGE TO HER GREATE GRANDMOTHER AND GRANDMOTHER 2 QUEENES BOTH NAMED ELIZABETH, TO HER MOTHER MARGARET Q.OF SCOTTS, TO HER AUNT MARYE THE FRENCHE Q, TO HER COUSYNS GERMANES MARY AND ELIZABETH QUEENES OF ENGLAND, TO HER NEECE AND DAUGHTER IN LAW MARY Q.OF SCOTTS. HENRY SECOND SONNE TO THIS LADY WAS K.OF SCOTTS AND FATHER TO JAMES THE 6 NOW KING. THIS HENRY WAS MURTHERED AT THE AGE OF 21 YEARES. CHARLES HER YOUNGEST SONNE WAS EARLE OF LEVENOX FATHER TO THE LADIE ARBELL. HE DYED AT THE AGE OF 21 YEARES AND IS HERE INTOMBED".

On the ledge at the east end was a Latin inscription, translated as:

"This work was completed at the charge of Thomas Fowler, the executor of this lady, 24 Oct 1578"

The inscription at the west end is also in Latin and can be translated:

"Sacred to the memory of MARGARET DOUGLAS, wife of Matthew Stuart, Earl of Lennox, granddaughter to Henry VII, King of England, by his daughter (Margaret Tudor): joined by the closest ties of kinship to most puissant kings, grandmother to James VI of Scotland, a lady of most pious character, invincible spirit, and matchless steadfastness. She died the tenth of March, year of Our Lord 1577. Margaret, mighty in virtue, mightier yet in lineage: ennobled by kings and by her forebears; descended from Scottish and English princes, she was also a progenitor of princes. Those things that belong unto death, she released to death most joyfully, and sought God, for she belonged to God before".

The monument was restored in the 1960s. At her feet is a crowned lion. Sculpted and painted coats of arms adorn the tomb chest: Darnley impaling Scotland at the east end; a lozenge of Angus and Douglas at the west end and at the sides Lennox impaling Angus and Douglas.