The King's Wardrobe, together with the Chamber, made up the personal part of medieval English government known as the King's household. Originally the room where the king's clothes, armour, and treasure were stored, the term was expanded to describe both its contents and the department of clerks who ran it. Early in the reign of Henry III the Wardrobe emerged out of the fragmentation of the Curia Regis to become the chief administrative and accounting department of the Household. The Wardrobe received regular block grants from the Exchequer for much of its history; in addition, however, the wardrobe treasure of gold and jewels enabled the king to make secret and rapid payments to fund his diplomatic and military operations, and for a time, in the 13th-14th centuries, it eclipsed the Exchequer as the chief spending department of central government.

There were in fact two main Wardrobes for much of this period: around 1300 the confusingly named Great Wardrobe, responsible only for expenditure on such things as clothing, textiles, furs and spices, split away from the more senior Wardrobe, which remained responsible for financing the king's personal expenditure and his military operations. In addition there were smaller Privy Wardrobes at various royal palaces; most of these provided items for the personal use of the king when in residence, but the Privy Wardrobe in the Tower of London came to specialize in the storage and manufacture of armour and armaments, and as such it too developed into an autonomous department of the State.

By the 15th century the Wardrobe had lost much of its earlier influence, and it eventually merged entirely into the Household and lost its separate identity. At the same time, the Great Wardrobe began to be referred to, more simply, as "the Wardrobe", to some extent taking on the identity of its forebear; but in the sixteenth century the Great Wardrobe lost its independence (it continued in existence as a subsidiary department within the Royal Household until it was abolished by the Civil List and Secret Service Money Act 1782).

In the Middle Ages persons of wealth and power often slept in a chamber (Latin camera), alongside which a secure room or wardrobe (garderoba) would be provided for storage of clothes and other valuables. In the royal household, the Chamber came to represent the king's nearest advisers. Before long the Wardrobe emerged, under the auspices of the Chamber, to become an administrative body in its own right, providing secure storage for the robes, treasures, archives and armaments of the king. Like other offices of the household it was an itinerant operation: carts and cases containing valuables travelled with the king and his court as they moved from place to place around the realm.

Prior to the 13th century references to the Wardrobe and its keepers are few. The 10th-century King Eadred bequeathed substantial sums of money in his will to his hrœgelthegns (robe-keepers), which may suggest that these were persons of some importance. By the reign of Henry II the king's Wardrobe is identified as a 'place of safe deposit' with its own staff, and its own premises within various royal palaces or strongholds; there remained, however, a good deal of functional overlap between the Chamber and the Wardrobe.

After 1200, however, the Wardrobe grew in activity and in prestige, partly as a result of King John's constant travelling of the realm, which required a more immediate source of funds than the fixed Exchequer. The Wardrobe first rivalled, and then eclipsed the Chamber in terms of power within the Court and in relation to the governance of the realm. Thus we see, early in the reign of Henry III, the office of Treasurer of the Chamber annexed to (and taken over by) that of Keeper of the Wardrobe. At around the same time the Keeper's deputy (the Controller of the Wardrobe) was given oversight of the Privy Seal (which had first come into use within the Chamber). This meant that the Wardrobe, which already served as a repository of important documents and Charters, began producing them as well; and thenceforward its Controller tended to be an important and trusted adviser to the king. With these developments, a third official, the Cofferer of the Wardrobe, began to take increasing responsibility for the day-to-day business of the Wardrobe.

The administrative historian T. F. Tout has speculated that a reason for the Wardrobe's increasing influence was its "new and elastic" nature: it was not hidebound by restrictive traditions or customary ways of working. Moreover, it was able to respond quickly in times when speedy expenditure was required – most especially in time of war – and with a flexibility which suited both the monarch and the nascent powers of English government. It did so largely by securing loans, on the basis of its valuable assets and treasures, from Italian bankers (the Riccardi and the Frescobaldi). In this way the Wardrobe became an independently powerful financial office.

There was however also a political dimension to the Wardrobe's rise. As G. M. Trevelyan put it, "If one office…was secured by the baronial opposition, the King could dive underground and still govern the country through the Wardrobe": hence the baronial demand in 1258 that all money should in future go through the Exchequer.