The trouble had started in 1332, when Edward Balliol invaded Scotland with Edward III's backing, exploiting the minority of David II. Balliol's outnumbered force won an improbable victory at Dupplin Moor, just outside Perth, on 11 August 1332. Balliol was crowned at Scone on 24 September, and from 1333 he ran his regime from Perth. In December he thanked Edward III by granting most of Southern Scotland to him outright. An English garrison was installed at Perth in 1335 after a fresh campaign by Balliol and Edward together. In 1336 Edward strengthened the town's defences by raising stone walls on three sides and three towers, requiring six nearby monasteries to pay for the work. The walls were new, but the strategic situation was deteriorating fast.

Thomas Ughtred left Hull on 12 March 1337 with 240 men to take command of the Perth garrison. The terms of his indenture allowed him 460 men in peacetime and 800 in war, although those numbers were never realistic. Within months Ughtred was writing south asking to be relieved of command. His men were not getting paid. They were not getting fed. The northern garrisons were increasingly difficult to supply across a hostile and rebellious countryside, and supplies had to come by sea from Hull and King's Lynn. From April 1339, a small French fleet hired by the Scots began to interdict the supply line. Whatever official confidence remained in the position was already, quietly, eroding.

Robert Stewart, the Guardian of Scotland and the future Robert II, began the siege in June 1339. The earls of Ross and March were with him. William Douglas joined them later, bringing the French pirate Hampyle and a force of exiled Scots from Chateau Gaillard, the same French castle where the young David II had been kept safe. French knights came with their retainers. Hampyle's barges blockaded the Tay estuary, cutting off the seaborne supply line that was Perth's only remaining lifeline. Miners provided by the Earl of Ross drained the town's moat. Attempts were made to undermine the walls. One of Hampyle's best ships was captured - either during the blockade or during an attempt to storm the town - and he had to mount a separate operation to get it back.

In parallel with the siege, Douglas pulled off a quieter victory. He convinced William Bullock, Balliol's commander at Cupar Castle in Fife, to switch sides in return for an award of land and possessions. The chronicler John of Fordun records that Bullock offered useful advice and brought appropriate help to the besiegers, including advising that the protective shelters be moved closer to the walls to better protect against crossbowmen. With supplies running out, with the moat drained, with the walls under attack, Ughtred capitulated on 17 August. The siege had lasted ten weeks. The English troops were allowed to return home, in a small mercy that says something about the limits of fourteenth-century retribution. In October a relief force of 1,264 men from Cumberland and Westmorland marched north under Balliol's command, but never reached Perth, instead spending three weeks raiding elsewhere in Scotland.

Ughtred faced accusations of cowardice when he got home, and in October 1339 succeeded in clearing his name before parliament. The Bruce faction next besieged Stirling Castle, although quarrels among the Scottish nobles caused the Earl of Ross to leave. Edinburgh fell back to the Bruce faction in 1341. David II returned from France in June. Stirling fell in 1342, Roxburgh in the same year. David was eventually captured in October 1346 at the battle of Neville's Cross in County Durham and held in England until 1357. Edward Balliol gave up his claim to the Scottish throne in 1356, pleading infirmity and old age, in exchange for an annuity of 2,000 pounds. He died in 1364. The walls of Perth, paid for by six monasteries to hold a king who was never quite king, came down piece by piece in the centuries that followed.