Atto was born in Portugal in 1070. In his 20’s he went to Italy as a pilgrim. He stopped by the Vallombrosa Abbey in Tuscany and was greeted there by the Abbot. By 1100 he became a Vallombrosian monk and by 1105 he became the Abbot. He progressed to Abbot General in 1120. He wrote about the lives of several Vallombrosaian Abbots one of which was the Bishop of Palma.
He became Bishop of Pistoia in 1135. That year he transferred relics of the Apostle James from Santiago de Compostela to Pistoia and dedicated an altar to St James in the Cathedral of St Zeno. This was to improve the economic growth of Pistoia as many pilgrims began to visit.
In 1337 his body was discovered in the Church of San Giovanni in Corte and was moved to the Cathedral of Saint Zeno. From the middle of the 17th century until the beginning of the 19th century fires and torches were lit in his honour in the Piazza Duomo.