He acquired fame as a lecturer at the University of Paris and also as a preacher when he entered the Order of Friars Minor, probably in 1224 or 1225.
When Haymo saw the Friars Minor he recognised the cord and, after having asked the advice of the Dominican Master General Jordan of Saxony, Haymo and three others entered the Friars Minor at St. Denis, just outside Paris, on Good Friday after having preached the Good Friday sermon.
Shortly after this he was appointed custos at Paris, in which capacity he seems to have attended the general chapter of the order at Assisi in 1230, and was one of the deputies sent by the chapter to Pope Gregory IX to petition for an explanation of certain points in the rule about which there had arisen some discussion in the order.
After this chapter Haymo probably went to England, for from a mention of him in the Patent Rolls Henrici III" he seems to have been at Oxford in 1232, probably as a lecturer in the Franciscan school there.
He led a peculiarly active life, for during these years he not only lectured at Oxford, but also at Tours, Bologna, and Padua.
After the deposition of Elias, Albert of Pisa, Provincial of England, was elected general, and Haymo succeeded him in the English provincialate.
Instead, he began to enlarge the Order's lands—particularly around Oxford's College of the Franciscans outside the old wall's Watergate—so that the friars would be able to work for their own sustenance instead of depending on charity.
Although very zealous for the poverty of the rule, he yet was aware of the disadvantages of depending too much on alms, preferring that the friars live by their own labours.