Specific details of the life of Peter Waldo are largely unknown.

Extant sources relate that he was a wealthy clothier and merchant from Lyons and a man of some learning.

Sometime shortly before the year 1160, he had been inspired by a series of events, firstly, after hearing a sermon on the life of St. Alexius, secondly, when rejection of transubstantiation was made a capital crime, thirdly, the sudden and unexpected death of a friend during an evening meal.

From this point onward, he had begun living a radical Christian life giving his property over to his wife, while the remainder of his belongings he distributed as alms to the poor.

At about this time, Waldo began to preach and teach publicly, based on his ideas of simplicity and poverty, notably that "No man can serve two masters, God and mammon" accompanied by strong condemnations of Papal excesses and Catholic dogmas, including purgatory and transubstantiation, while accusing them of being the harlot from the book of Revelation.

By 1170, he has gathered a large number of followers who are referred to as the Poor of Lyons, the Poor of Lombardy, or the Poor of God, who spread their teaching abroad while disguised as peddlers.

Often referred to as the Waldensians (or Waldenses), they are distinct from the Albigensians or Cathari.