The square's story begins with a real estate bet. In 1662, Charles II extended a lease over 45 acres of Pall Mall Field to Henry Jermyn, 1st Earl of St Albans, who immediately set about creating something extraordinary. The location had one obvious advantage: it sat conveniently between the royal palaces of Whitehall and St James, making it irresistible to the aristocracy who needed to be near the court. By the 1720s, seven dukes and seven earls were in residence—a concentration of hereditary power that London has never quite matched since. The houses looked deceptively modest from the street, but behind those facades lay something remarkable: deep plots, high ceilings, and spaces engineered for grandeur. Robert Adam, Matthew Brettingham, and John Soane all worked here, leaving interiors that matched the ambitions of the people who commissioned them.

What happened inside these houses shaped the world. At Number 31—Norfolk House, a neo-Georgian replacement for the Duke of Norfolk's original mansion, demolished in 1938—the Allied forces planned Operation Torch and Operation Overlord, the landings that turned the tide of the Second World War. Eisenhower used it as his London headquarters. Number 10, now home to Chatham House, the global policy institute, is where three prime ministers once lived. Number 12 was Ada Lovelace's London home from 1837—the mathematician who wrote the first algorithm now considered a foundational figure of computing history. Number 4 housed Nancy Astor, the first woman to sit in the House of Commons. The square's residents did not merely witness history; they made it.

On 17 April 1984, the square's long diplomatic history turned violent. Number 5—then serving as Libya's People's Bureau—became the scene of a shooting that shocked Britain. During a protest outside the building, shots were fired from a window inside, killing Police Constable Yvonne Fletcher, who was managing the demonstration. She was 25 years old. The Libyan Embassy Siege that followed lasted eleven days, ending only when the Libyan diplomats were expelled from Britain. A small memorial marks the spot where Fletcher fell, a few metres from the pavement where she had stood. It is easy to walk past it without noticing, which is perhaps why those who know the square always pause there.

At the heart of the square sits a walled garden, opened to the public on weekdays, overseen since 1726 by the St James's Square Trust—the earliest statute ever passed to regulate a London square, and the only one still operating unamended. An equestrian statue of William III, erected in 1808, dominates the space. The garden feels private even when it is public, a quality the square has always cultivated. The London Library, one of the world's great lending libraries with over a million volumes, has been at Number 14 since 1845. BP and Rio Tinto hold offices here. The square has shifted from aristocratic residence to institutional home, but its weight—its sense that what happens inside these walls matters—has not diminished.