A quick work was done in his heart and God began to raise him up to preach the Gospel. Beside Irish he mastered English, Latin, Greek and Hebrew. While John Wesley was on a three month preaching tour of Ireland Thom-as talked to him concerning the call of God. He was soon preaching twice every day on the streets of Limerick. Souls who heard him began to come under deep conviction of sin and as a result were saved. He left his work as a schoolteacher and began to travel to preach to little groups of scattered believers which began to grow and thrive. His sermons were rarely less than an hour and were as loud as they were long. He would preach two and three times a day in the open-air with great success. People would drop to their knees and cry out for mercy. He preached on mountains and highways, in meadows, private houses, prisons and ships. He was attacked and frequently had to run for his life from a stone-throwing mob.
In 1752 Wesley held his first Irish Leaders Conference in Limerick. Thomas was one of only nine itinerant preachers in Ireland. He was given responsibility for Dublin, Cork, Limerick and those counties around Belfast in the North. He travelled with Wesley preaching by his side to large gatherings. In 1754 he attended the main Methodist conference in London. Wesley said of him that he did not know any preacher who in so few years was the instrument of converting so many sinners from the error of their ways. He also said of him “Such a master of Biblical knowledge I never saw before, and never expect to see again.” He believed that if he had six men like Thomas Walsh he would turn England upside down. After only nine years as a Christian Thomas went to his reward at the age of just twenty eight. He had literally worn out his body in abundant labours.