| William VIII, Marquis of Montferrat | |
| Succession: | Marquis of Montferrat |
| Reign: | 1464–1483 |
| Predecessor: | John IV Palaiologos |
| Successor: | Boniface III Palaiologos |
| Noble Family: | Palaeologus-Montferrat |
| Father: | John Jacob, Marquis of Montferrat |
| Mother: | Joanna of Savoy |
| Spouse: | Marie de Foix Elisabetta Sforza Bernarde de Brosse |
| Issue: | Giovanna Blanche of Montferrat |
| Birth Date: | 19 July 1420 |
| Birth Place: | Casale Monferrato |
| Death Place: | Casale Monferrato |
William VIII Palaiologos (Italian: Guglielmo VIII Paleologo; 19 July 1420 – 27 February 1483) was the Marquis of Montferrat from 1464 until his death.
He was the second son of Marquis John Jacob and Joanna of Savoy, daughter of Amadeus VI of Savoy.
William inherited the Marquisate after the death of his elder brother John IV. He obtained, by Emperor Frederick III, the territories lost to Savoy from 1435. William served as condottiero for Francesco I Sforza of Milan and fought alongside him at the battle of Caravaggio(1448) and was afterwards rewarded with the lordship of Alessandria.
In 1449, William was accused of treachery and imprisoned by Francesco Sforza. The reason was said to because he had formed an attachment to Sforza's wife Bianca Maria Visconti. He was released a year later. Angry over his treatment by Sforza, William encouraged his brother John IV of Montferrat and relative Louis of Savoy to make war on Sforza (and Milan), and then he himself would lead the troops in battle. This attempt failed.
William later became a tutor to the couple's son Galeazzo Maria. Following his assassination, William held several positions in the Duchy of Milan.
William married on 19 January 1465, Marie de Foix (d.1467), daughter of Gaston IV, Count of Foix; and secondly on 18 July 1469, Elisabetta Sforza (d.1473), daughter of Francesco I Duke of Milan and Bianca Maria Visconti; and finally, on 6 January 1474, Bernarde de Brosse daughter of Jean II de Brosse.
His second marriage to Elisabetta Sforza, they had:
When William died in Casale Monferrato, he was succeeded by his brother Boniface III.