A studious and deeply religious boy, it had seemed likely that he would 'take the gown' and receive Anglican ordination. However under the influence of Adam Clarke and other visiting Methodist preachers he came in 1800 to a clear realisation that the Calvinistic doctrine of unconditional election and reprobation enshrined in the Thirty-nine Articles was false. Almost immediately he became a local preacher and on 13 February 1801, a national fast day, experienced a vision convincing him that he should become a full time evangelist. Yet it was a time for him of much spiritual oscillation and as a moderately prosperous young farmer in 1803 he married (see below). He abandoned his vision of being an evangelist when his son Ebenezer William was born in 1804. In 1807 he gave a plot of land at Gunwen and helped to build a new chapel on the site, which he ensured was secured as a Wesleyan chapel in the Bodmin circuit. In 1808 his son died (the tombstone can be seen towards the rear of the present (1869) Gunwen chapel) and that led him to radically reconsider his call to be an evangelist.
He may have engaged in some evangelizing, but when he proposed in 1808 an independent campaign in west Cornwall Joseph Womersley, one of the two preachers in the Bodmin circuit, persuaded him that he would be better advised to offer for regular ministry. However, Edward Millward, the Superintendent, opposed him and when he did offer in 1810 he was rejected by the Cornwall District Meeting because of his family responsibilities. Meanwhile he had actively developed into an itinerant free-lance evangelist. When Womersley was away at the 1808 Conference, O'Bryan filled his appointments. In this period he heard that at the then small fishing village of Newquay there was no Methodist preaching. Going there on his own initiative he was soon able to form a society, but without laying on them the obligations of accepting all the Wesleyan rules or paying any form of assessment. After his rejection for the ministry things came to a head when at theBodmin quarterly meeting following his rejection he proposed that the ministry should be supported by voluntary contributions. The reaction to this proposal led to action over the Newquay society and others in the area. They were told that O'Bryan was not a Methodist (untrue at that point) and that they should accept the rules. It seems that they did, but O'Bryan had no more to do with them.
O'Bryan was expelled from the Methodist societies in November 1810. It happened at Gunwen chapel itself, at the hand of William Prosser, the second minister. The charge was one of indiscipline. Several of O'Bryan's supporters went with him. The area to which he turned was along the western side of Bodmin Moor, and here he created a line of societies and preaching places independent of WM. He was doing what he did best, preaching the gospel in the fresh ground on the fringes of the WM circuits. In March 1814 his wife Catherine took a shop at St. Blazey, within the area of the St. Austell Circuit, in order to fund William's desire to commit himself to full-time evangelism. In the same year James Odgers, the new Superintendent of the Bodmin circuit, took opportunity to seek a reconciliation with O'Bryan, and his new societies were integrated into that circuit. O'Bryan and Catherine became members in the St. Austell circuit. Yet that only left him free to fly off to further new opportunities. One of several Home Mission stations promoted in 1805 by Thomas Coke was the Stratton Mission, working from 1811 in the north Devon area inland from Stratton near Bude previously untouched by Methodism (later in the Holsworthy Circuit). It was to this circuit that O'Bryan came. The superintendent, William Sutcliffe, was very short-handed and welcomed O'Bryan's help at first. However, O'Bryan's relationship with Sutcliffe became more and more strained on account of his disregard of Methodist rules and his apparent self-sufficiency. When Sutcliffe was reprimanded by the District meeting for using O'Bryan at all, his use of O'Bryan officially had to cease.
Meanwhile O'Bryan's membership ticket in the St. Austell circuit had been withdrawn on the grounds that he had not attended class for three weeks. For the second time he found himself expelled.Yet he had his supporters, most notably Richard Spettigue, the circuit steward, and in the societies he had planted. And in spite of the active opposition of George Banwell, Sutcliffe's successor in 1815, O'Bryan continued his evangelizing activities. At the Stratton quarterly meeting Spettigue made a proposal to the circuit which would have given him some recognition within the circuit and at the same time allowed him to pursue his independent mission work. This was not acceptable to Banwell. Thus on October 1st 1815 O'Bryan wrote: 'I entered on my circuit at Mary-Week and Hex.' He had become a church founder. Within a week 22 members had been enrolled at Lake Farm, Shebbear, among them the teenager James Thorne.
The following decade witnessed the rapid spread of the BC movement, but also the deteriorating relationship between O'Bryan and his followers, which led to a final break in 1829. A man gifted and blessed as an evangelist, but with a persistent autocratic tendency was not the most diplomatic leader of an infant church. His followers called themselves Arminian Bible Christians, but in 1831 O'Bryan emigrated to North America, residing there in self-imposed exile for the rest of his life. O'Bryan held the roles of Chapel Fund Treasurer 1825-1826, Editor 1825-1826, Missionary Secretary 1821, 1824 and 1827 and Treasurer 1826, and was President of the Conference from 1815 to 1827.
His wife Catherine O'Bryan, (née Cowlin, 1781-1860) came from a prosperous Anglican family at Perranzabuloe, but having been converted among the Wesleyans she joined the society at Bolingey near Perranzabuloe at the age of eighteen. She was helping to manage her father's draper's shop in Roche, near St. Austell, when she met O'Bryan at a prayer meeting in 1800. They were married on a hot July day in 1803 in the sand-enveloped church on the Perranzabuloe sands (the name is Cornish for St. Piran's Church on the Sands). It was the last wedding to take place there before that medieval church was dismantled and then rebuilt two miles inland where it stands today.
Catherine became one of his helpers, first in the group of societies he created along the western side of Bodmin Moor. At Millpool, north of Cardingham and about half a mile south of the modern A30, she responded to a need and became a preacher. She thus became the first of the many females who worked alongside O'Bryan. She was able to help her husband in many ways, and followed up Mary Toms' pioneering visit to the Isle of Wight in 1823. However she never appeared on the BC stations. She emigrated with O'Bryan to America in 1831. She wrote poetry and, it is thought, a few hymns, including possibly some otherwise unidentified in the 1820 and 1824 hymn books. Catherine died in New York in 1860.Their daughter Mary O'Bryan became a BC itinerant, and pioneered the work in London and Guernsey and followed her mother to the Isle of Wight in 1824. She marriedSamuel Thorne in 1825, and stayed in England. Two other daughters, Eden and Thomazine preceded their parents to America in 1830, and a third, Serena, appears to have travelled with them. All stayed in America. Thomazine was married in New York and died in Baltimore.John Hicks Eynon, on furlough from the Canadian Mission and on a preaching tour, met O'Bryan, to Eynon's surprise it would seem, on the Scilly Packet. O'Bryan preached in the morning at the chapel on St.Mary's, and Eynon in the afternoon and evening. O'Bryan regularly complained that the annuity he had been promised for surrendering his copyright in the hymn book to the BC Conference arrived late. He died in New York on 8 January 1868 and is buried in the Greenwood cemetery, Brooklyn, where he is named 'Bryant', having dropped his preference for what he had supposed to be the correct form.