Henry Stuart, Lord Darnley (1546 – 10 February 1567) was King of Scotland as the second husband of Mary, Queen of Scots, from 29 July 1565 until his murder. Darnley had one child with Mary, James VI of Scotland and I of England. Less than a year after the birth of his son, Darnley was murdered at Kirk o' Field in 1567. Many contemporary narratives describing his life and death refer to him as simply Lord Darnley, his title as heir apparent to the Earldom of Lennox.

He was the second but eldest surviving son of Matthew Stewart, 4th Earl of Lennox and his wife Lady Margaret Douglas, which supported his claim to the English succession. Darnley's maternal grandparents were Archibald Douglas, 6th Earl of Angus, and Queen Margaret Tudor, daughter of King Henry VII of England and widow of King James IV of Scotland.^{[citation needed]}

Henry Stuart, Lord Darnley was born at Temple Newsam, Leeds, in the West Riding of Yorkshire, England, in 1546. Henry was initially believed to be born on 5 December 1545, but more recent research suggests he was born in 1546, as his mother had given birth in late February 1545. In a letter from March 1566, his age was given as nineteen.

In 1545, his father, Matthew Stewart, 4th Earl of Lennox, was found guilty of treason in Scotland for siding with the English in the War of the Rough Wooing, in opposing Mary of Guise and Regent Arran. The family's Scottish estates were forfeited and his father went into exile in England for 22 years, returning to Scotland in 1564. The Countess of Lennox Margaret Douglas, his mother, had left Scotland in 1528.

The Scottish scholar John Elder was among his tutors. Elder advocated Anglo-Scottish union through the marriage of Mary, Queen of Scots, and Prince Edward. His advice to Henry VIII in 1543, was termed the Advice of a Redshank. Another schoolmaster to the young heir was Arthur Lallart, who would later be interrogated in London for having gone to Scotland in 1562.

Henry was considered strong, athletic, skilled in horsemanship and weaponry, and passionate about hunting and hawking. His youthful character is captured somewhat in a letter of March 1554 to Mary I of England from Temple Newsam, where he writes about making a map, the Utopia Nova, and his wish that "every haire in my heade for to be a wourthy souldiour". In Scotland, he was delighted with an English Water Spaniel, a gift from the courtier James Melville of Halhill.

There was a political dilemma in England arising from the dynastic ambition of the Lennoxes: Matthew Stewart, 4th Earl of Lennox, was third in line to the Scottish throne, and his wife Margaret Douglas, Countess of Lennox, was a niece of Henry VIII, making her a potential successor to the English throne if Elizabeth should die. As Roman Catholics, they posed a threat to English Protestants. Although Elizabeth was bright, witty, and well-educated for her position, as a woman she had to prove herself. As she was a Protestant, many Roman Catholics would have liked to see the Catholic Mary, Queen of Scots, take the throne. They regarded Elizabeth as illegitimate, her parents' marriage not having been recognised by the Catholic Church. As a male descended from Henry VII, Darnley was also a contender for the English throne—these interrelationships made for complex intrigues, spying, strategising, and manoeuvering for power at the various courts.

When Henry II of France died in July 1559, Lennox's brother John, 5th Sieur d'Aubigny, was elevated in the French court as a relative of the new French queen, Mary, already Queen of Scots. Aubigny arranged for Darnley to be dispatched to the French court to congratulate Mary and Francis II of France on Francis's accession and seek restoration for Lennox. Mary did not restore Lennox to his Scottish earldom. Still, she did give 1,000 crowns to Darnley and invited him to her coronation. Lennox planned to appeal directly to the Queen of Scots via her ambassador, over the heads of Elizabeth and the Guise. The mission of Lennox's agent, one Nesbit, appears to have been a desperate one; not only was Lennox willing to hand over Darnley and his brother Charles as hostages for his restoration, but he supplied pedigrees of Darnley, indicating his right to the inheritance of England and Scotland and the houses of Hamilton and Douglas. Aubigny was also later accused of supporting Mary's title to the throne of England and hinting that even his nephew had a stronger claim than Elizabeth.