Tamworth's story begins not with stone walls but with power. When Offa became ruler of Mercia in the late eighth century, he made Tamworth his chief residence, a palace from which he dominated much of England south of the Humber. The earliest known charter issued from Tamworth dates from 781. But the Viking Great Army swept through in 874, leaving the town a smoking ruin for nearly forty years. Recovery came in 913, when Aethelflad, Lady of the Mercians and daughter of Alfred the Great, rebuilt Tamworth with an earthen burh, a fortified enclosure designed to resist Scandinavian raiders. The Danes sacked it again in 943 regardless, and Tamworth's days as a royal seat faded. But the site's strategic importance endured. A mint struck coins for Anglo-Saxon kings through the late tenth century, and when William the Conqueror needed to consolidate his grip on central England, Tamworth was among the places he chose to fortify.

William granted Tamworth to his steward Robert Despenser, who built a wooden castle on the old Saxon mound in the 1080s. When Robert died childless, the estate passed through his niece Matilda to Robert Marmion, beginning the most colourful chapter in the castle's history. The Marmion family, hereditary champions of the Dukes of Normandy, held Tamworth for six generations, from roughly 1100 to 1294, and it was under their watch that the wooden defences gave way to stone. The relationship was not always smooth. The third Baron Marmion deserted King John in 1215, prompting the king to order the castle demolished and Marmion's son imprisoned. The demolition never happened, but the threat reveals how closely castles and loyalty were bound in medieval England. Walter Scott later borrowed the Marmion name for his 1808 narrative poem, proclaiming its fictional hero 'Lord of Fontenaye, Of Tamworth tower and town,' though the real barony had been extinct for centuries.

The castle's defences, built for medieval warfare, proved inadequate when the English Civil War arrived. Parliamentary forces captured Tamworth on 25 June 1643 after just a two-day siege. A garrison of ten officers and 77 soldiers held it for Parliament through 1645 under military governor Waldyve Willington. Ironically, this occupation saved the castle from the slighting, the deliberate destruction, that Parliament ordered for so many Royalist strongholds. Having served their purposes, the Parliamentarians left it standing. The castle passed through the Ferrers, Shirleys, and Comptons over the following centuries, falling in and out of repair as fortunes rose and fell. J.M.W. Turner painted it from the southeast in 1832, capturing the castle mill along the Anker and the Lady Bridge in a panoramic watercolour. By 1891, the Marquess Townshend put the castle up for auction, and Tamworth Corporation bought it for three thousand pounds in 1897 to celebrate Queen Victoria's Diamond Jubilee.

Today Tamworth Castle operates as a museum, its rooms tracing the layered history of the site from Saxon palace to Norman stronghold to Jacobean residence. The shell keep contains a twelfth-century gate tower and residential buildings spanning five centuries: a thirteenth-century north range, a fifteenth-century oak-timbered Great Hall, and a seventeenth-century Jacobean south range. The heraldic arms of the Ferrers family and their marriage connections dominate the interior, a genealogical tapestry in stone and wood. Henry I visited between 1109 and 1115; Henry II came in 1158 with Thomas Becket in tow. The castle stands as proof that English history is not something that happened elsewhere and got written about. Sometimes it happened on a riverbank in Staffordshire, quietly, persistently, for more than a thousand years.