Guido Tarlati (died 1327) was a lord and Bishop of Arezzo.
Tarlati, coming from a Ghibelline family of Pietramala, became bishop of 1312. In 1321 he was declared seignior of Arezzo, a position he held until his death. During his administration the city had generally good relations with its neighbors Florence and Siena, and promoted the pacification between the Guelphs and Ghibellines. Later he supported Uguccione della Faggiola and Castruccio Castracani, lords of Lucca, in their wars against Florence.
Tarlati also expanded the territories of Arezzo, and in 1323, with the collaboration of Francesco I Ordelaffi (Ghibelline lord of Forlì), he conquered Città di Castello. Arezzo's expansion caused however the deterioration of the relations with the Papal States, ending with the excommunicated of Tarlati by Pope John XXII. He was replaced by another bishop, Boso Ubertini, but Tarlati did not allow him to enter in the city. Tarlati's prestige at the time was so high that German emperor Louis IV wanted to receive from him the Iron Crown.
A short time before his death Tarlati reconciled with the Pope. According to Giorgio Vasari the tomb commissioned by Guido's brother, the condottiero Pier Saccone Tarlati di Pietramala, was designed by Giotto (although this is disputed), who recommended to Pier Saccone the Sienese sculptors Agnolo da Ventura and Agostino di Giovanni to execute it. It is located in the Cathedral of Arezzo.