Müller moved to Bristol on 25 May 1832, and alongside his good friend Henry Craik, began working at Bethesda Chapel. The two would take it in turns to preach, with one taking the morning sermon and the other preaching in the evening, and each week would see them swap roles. They attracted large crowds of people from the beginning of their time at Bethesda, because of their strong preaching and the novelty of hearing either a thick Scottish accent or thick German accent when they spoke!
The two friends began to set aside evenings in the chapel to talk with people individually, an important pastoral practice which they continued throughout their lives. They also saw the congregation grow in faith and in number throughout their years of pastoring at Bethesda. Müller continued to preach at Bethesda Chapel for the rest of his life, even while devoted to his other ministries.