The origin of St Ives is attributed in legend to the arrival of the Irish Saint Ia of Cornwall, in the 5th century. The parish church bears her name, and St Ives derives from it.
The Sloop Inn, which lies on the wharf was a fisherman's pub for many centuries and is dated to "circa 1312", making it one of the oldest inns in Cornwall. The town was the site of a particularly notable atrocity during the Prayer Book rebellion of 1549. The English Provost Marshal (Anthony Kingston) came to St Ives and invited the portreeve, John Payne, to lunch at an inn. He asked the portreeve to have the gallows erected during the course of the lunch. Afterwards the portreeve and the Provost Marshal walked down to the gallows; the Provost Marshal then ordered the portreeve to mount the gallows. The portreeve was then hanged for being a "busy rebel".
The seal of St Ives is Argent, an ivy branch overspreading the whole field Vert, with the legendSigillum Burgi St. Ives in Com. Cornub. 1690.
During the Spanish Armada of 1597 two Spanish ships, a bark and a pinnace had made their way to St Ives to seek shelter from the storm which had dispersed the Spanish fleet. They were captured by the English warship Warpsite of Sir Walter Raleigh leaking from the same storm. The information given by the prisoners was vital on learning the Armada's objectives