The mantle of Garretson fell upon Black and he was again compelled to lead the forces, and take the initiative in opening up new places and preaching at every opportunity. Aroused by the sad spiritual condition of the people, he spared not himself in excessive labors, and so successful were his efforts for the conversion of souls, that John Wesley became more concerned than ever, in the affairs in the Maritime Provinces and Newfoundland. Dr. Coke who constituted in his own person the Methodist Missionary Society, was commissioned by Wesley to visit Nova Scotia, and he embarked on September 24th, 1786, with three missionaries for Nova Scotia, but a dangerous storm which cast the vessel on the ocean for nearly two and a half months, compelled them to land at Antigua, in the West Indies, and Black was left without the promised help, as the missionaries remained there, and a new era of successful missions was begun. His field was large enough surely, for Wesley had said in a letter to him dated London, Oct.15, 1784, "Your present parish is wide enough, namely Nova Scotia and Newfoundland. I do not advise you to go any further." During the year 1786, there was a great revival in Liverpool under John Mann, a church had been erected in Halifax in which William Black preached for the first time on Easter Sunday, and at Barrington and Horton, there were several notable conversions, still through lack of missionaries, there could not be given any assistance to Cumberland, Annapolis, Digby, and the whole Province of New Brunswick. He was however greatly encouraged by a visit to Liverpool where the revival was in progress, and by good news from River Philip, where his eldest brother John had settled as a farmer, and who had begun to exercise his gifts as a local preacher, and with so great success, that at one meeting, ten persons rejoiced in having found Christ.

At the second District meeting held on October 15th, 1787, in Halifax, there were present, William Black, William Grandine, William Jessop, and the two brothers, John and James Mann, who had come from the United States to labor as missionaries in Nova Scotia. After the third District Meeting which was held in the May following, William Black spent about a month visiting Shelburne, Barrington, Cape , Port La Tour and Port Medway, and when he returned to Halifax, he was greatly encouraged by the good work which had gone on under James Mann's labors during his absence. Meanwhile, the Rev. James Wray had been sent out from England with a general charge to superintend the work, as William Black and the other missionaries had not been ordained, and could not therefore dispense the sacraments, but the relations between Wray and Black became somewhat strained, and threatened seriously to interfere with the advance of the Kingdom of God. With good judgment and much patience William Black laid the whole matter before John Wesley, but without his counsel the breach was healed, and they labored again in harmony. James Wray felt that the duties of superintending the work in the Province were too onerous for him, and he requested to be relieved of the position, and Dr. Coke appointed William Black, Superintendent of the Methodist Church in the Maritime Provinces and Newfoundland, James Wray removing to the West Indies, where he died in 1790.

The growth of Methodism was somewhat retarded by the fact that William Black had not been ordained, and consequently could not dispense the sacraments, and it was felt that his influence would greatly extend were he to assume all the responsibilities of a Christian minister. An opportunity was afforded him of being ordained, by the presence of Dr. Coke at the Conference held in Philadelphia in 1789, and accompanied by John and James Mann, who went for the same purpose, he attended the Conference, and on May 19th he was ordained a Deacon, and on the following day, an Elder. During a month spent in that city, he lost no opportunity of seeking to do good, and was cheered by learning of some being blest, among whom was a lady who had been converted under a sermon preached there by him, during his previous visit in 1784.

In a report sent to John Wesley during the year, there are shown gratifying results of the labors of the missionaries in Nova Scotia, as the church in Halifax had grown in numbers and spirituality, and throughout the Province there were about five hundred members, and with pardonable pride and joy, William Black remarks, how greatly he was comforted, as the church had grown in two years, "eight times larger, and eight times more serious and spiritual." The care of the churches pressed so heavily upon his soul, and there was so great need of additional missionaries to meet the growing demands of the wide field, that William Black hastened to Philadelphia to consult Dr. Coke, and had the pleasure of attending the Conference held in that city commencing on May 17th, 1791, at which the venerable Bishop Asbury presided. The following week, he attended the New York Conference, when six missionaries were appointed to labor in Nova Scotia. About three weeks after his return home, he went on a visit to Newfoundland, which was marked by a gracious revival, and the cause of Methodism in the ancient colony was saved.

The story of Methodism in Newfoundland, reads like a bit of romance. The first missionary Lawrence Coughlan went there in 1765, and remained seven years, amid great persecutions, being prosecuted in the highest court, an attempt made to poison him, yet not only was he able to rejoice in many conversions, but his enemies were silenced, as the Governor acquitted him, and made him a justice of the peace. His health failed, and he was compelled to return to England. His ministrations in Newfoundland however led to the founding of Methodism in the Channel Islands, as Pierre Le Sueur, a native of Jersey, during a visit to Newfoundland was deeply convinced of sin under a sermon which Coughlan preached, and when he returned to his home, spoke of the knowledge which he had received, but his friends thought him mad. When John Fentin, a recent convert, returned from Newfoundland to Jersey, Le Sueur and his wife found peace to their souls through Fentin's instructions and prayers, and a great revival commenced, which swept through the islands, and laid the foundations of religion, which have continued till the present time. After Coughlan's departure, John McGeary was sent to fill the vacancy but all that was left of the good work were a few women, and he suffered so many hardships and witnessed so little fruit of his labors that he became so despondent, as to entertain serious thoughts of abandoning the field. William Black arrived in St. John's on August 10th 1791, and spent one day in the city, during which he waited upon the Presbyterian minister, the Rev. Mr. Jones, who was a man of catholic spirit, and whose spiritual life was deep and genuine. The next day he went to Carbonear, where John McGeary was stationed, whom he found "weeping before the Lord over my lonely situation and the darkness of the people," and when he began to preach, a great revival followed, and Methodism in the colony was saved from disaster.

The power of God fell upon the people at the very first service, and many were deeply convinced of sin at every meeting. At Carbonear the people cried aloud for mercy, so that he had to stop preaching, and betook himself to prayer, when the sound of his voice was nearly drowned by the people weeping, and he came down from the pulpit and passed up and down through the church, exhorting and directing them, as many as three and four persons being in an agony of spirit in every pew. Even after the service closed, the cries and groans of anxious persons could be heard at a considerable distance up and down the harbour. At Harbor Grace, Port a Grave, Bay Roberts and other places, similar scenes were witnessed, of deep conviction for sin, and many rejoicing in the knowledge of sins forgiven. At Conception Bay during a short time spent there, two hundred souls were converted, but that was not all, for throughout the colony, William Black marched in triumph, and saw very many souls won for Christ. It is no wonder that he considered this visit to Newfoundland, as "the most useful and interesting portion of his missionary life." The Rev. Richard Knight, who spent seventeen years in the colony says, that he "organized Methodism, settled the mission property, and secured it to the Connexion, increased and inspirited the society, and obtained for them the help they needed." Such a messenger could not fail to leave a deep and abiding impression upon the hearts of the people, and his departure was pathetic, as he stood for nearly an hour shaking hands with them, and at last as he tore himself away, he says, that he "left them weeping as for an only son." He secured fresh laborers from Wesley to carry on the work, and Methodism in Newfoundland was established upon a firm basis, and has continued vigorous till the present day.

Upon his arrival in Halifax he found that the gentleman who owned the church property in the city, had severed his connection with the society, and become a bitter opponent, but William Black though sorely tried, was in no wise daunted, and immediately he started a subscription list, and secured prompt and efficient help, so as to proceed with the building of a new church. One hundred pounds were raised in one day, and the society took fresh courage, and grew in numbers and strength. Having set matters in order in the city he visited Horton, Granville, Annapolis and Digby on his way to St. John, New Brunswick, where Abraham John Bishop was stationed, who arrived there in September 1791, and a week later organized the first class meeting in the city. Previous to that time several Methodist ministers had visited the then growing town, through the earnest solicitations of Stephen Humbert, a United Empire Loyalist, who landed there on May 18th, 1783. He was a New Jersey Methodist and desirous of having a society formed there. William Black arrived in November, 1791, and at once began to preach, but having seen some shipbuilders at work on the Sabbath, he denounced their action in a sermon on the same evening. A provincial statute existed forbidding anyone from exercising the functions of the ministry without a license from the Governor, and this was used to silence the courageous preacher. Undeterred by this opposition, and hindered from preaching, he spent his time visiting from house to house with blessed results. Three months later he visited St. John with permission to preach, and found a gracious revival in progress, then going to Fredericton he met a class of twenty-two, most of whom were soldiers, and during the few days spent there several conversions took place. On his return journey he visited St. Stephens, where Duncan McColl was the missionary, and he rejoiced in the evidences of growth, under the faithful labours of that devoted man of God, and this notable tour, closed with a farewell service in May to Abraham John Bishop. It was a touching scene, the people being much distressed at losing the young missionary, and well might they grieve, for after one year spent in Sheffield, he went to the West Indies to labor among the colored people and died at Grenada the following year. And thus passed away one who was esteemed as an eminently holy man, and William Black was bathed in tears.