He went into the ministry because his dear brother had hoped before he died, that his younger brother would become a minister of Christ. However, by the time he finished his studies, he had a passion for Christ and a passion to win souls, both of which he did not have when he went to Divinity Hall. In the spring and autumn of 1835, he went for examination by the Presbytery of Edinburgh. He had many ministers asking him to come and join them in their area, and he was particularly interested in the invitation of John Bonar, the minister of Larbert and Dunipace, near Stirling. He transferred to the Presbytery of Annan, Dumfries because they were less busy, so he was able to complete his public trials more quickly. He became licensed to preach on July 1st 1835; he records in his diary, "Preached three probationary discourses in Annan Church, and, after an examination in Hebrew, was solemnly licensed to preach the Gospel by Mr Monylaws, the Moderator. 'Bless the Lord, O my soul; and all that is within me be stirred up to praise and magnify his holy name!' What I have so long desired as the highest honour of man thou at length givest me--me who dare scarcely use the words of Paul, ‘Unto me who am less than the least of all saints is this grace given, that I should preach the unsearchable riches of Christ.’ Felt somewhat solemnised, though unable to feel my unworthiness as I ought. Be clothed with humility."
McCheyne preached for the first time at Ruthwell Church, Dumfries, the following Sunday. He wrote, ' Found it a more awfully solemn thing than I had imagined to announce Christ authoritatively; yet a glorious privilege!’ The next Saturday he wrote, "Lord, put me into thy service when and where thou pleasest. In thy hand all my qualities will be put to their appropriate end. Let me, then, have no anxieties." (It is rather strange that people in those days thought that they should speak to God in a form of King James Bible English, even though people did not even speak like that at the beginning of the seventeenth century.)
He began work at Larbert in November 1835, trusting in the Lord that he was in the right place. "It has always been my aim, and it is my prayer, to have no plans with regard to myself well assured as I am, that the place where the Saviour sees meet to place me, must ever be the best place for me." As Bonar’s assistant it was his job to preach alternated Sundays in Larbert and Dunipace and to visit as many of the population (there were 6,000 in the parish) as he felt necessary. Larbert was the parish of the great minister, Robert Bruce, back in the seventeenth century.
McCheyne would spend each morning at his private devotions, as preparation worth the work ahead that day. He particularly loved reading the Bible and also the works of Jonathan Edwards. He preached what he had experienced from God that day or week. There was more work for him to do there than he could handle. The several collieries and the iron works were full of those who were not Christians. He would later support the scheme to build more churches, and it was probably in the parish of Larbert where he got his understanding of the shortage of ministers in the nation. At the end of the year he developed a bad cough, so that he had to rest for several weeks. He wanted to spend the time in intercession, however, "I feel distinctly that the whole of my labour during this season of sickness and pain, should be in the way of prayer and intercession, And yet, so strongly does Satan work in our deceitful hearts, I scarcely remember a season wherein I have been more averse to these duties.” There were fears that he had damaged lungs, but he recovered and resumed his work. On returning he went to live in Carronvale, but he felt guilty that, because he was still weak, he was unable to do the work of a fit man. He particularly regretted that he was not more diligent in his work among the nearby collier workers.
McCheyne did not like the custom of reading sermons as it dulled the natural passion of the deliverer. He also disliked memorising a sermon, so he used to memorise the substance of the talk, but then speak according to how the Holy Spirit led him. One day he lost his written sermons as he rode quickly to Dunipace, so he had to speak without notes. He was amazed at how well he was able to speak, so he continued speaking in that way from then on, realising that it was better to rely on God, rather than the diligence of preparing the sermon. He began to speak from the heart rather than the head, so the fruit from his sermons increased substantially. He used to grieve if he had spoken with anything less than solemn compassion. On one occasion, he asked a friend what his last Sabbath's subject had been. It had been, "The wicked shall be turned into hell." On hearing this awful text, he asked, "Were you able to preach it with tenderness?"
In April 1836 he went to hear Alexander Duff in Stirling. Hearing Duff speak of his work in India opened up in McCheyne again a desire for missionary work, so he told the Lord that he was ready to go to India if that was what He wanted. But the Lord wanted him to do something else. In August he went to St Peter’s, Dundee as a candidate for pastor. He gave three sermons; his mind was not really on it in the first, he felt things went better in the second, but in the evening he gave his heart. Two people were converted in that service, the first known salvation fruits of his ministry. It is not surprising that he was unanimously voted in as Pastor. He would have preferred a country parish, but he recognised the call, although wondering why the Lord did not choose a stronger man for the position. After returning from his interview at St Peter’s, he records that there was more than usual anxiety in his girls class at Dunipace, and one girl was converted. It is interesting that this happened just as he was leaving for Dundee.