Pioneer evangelist and administrator. He first heard the present truth preached by J. N. Andrews in September 1852 at Rochester, New York, and was immediately convinced of the seventh-day Sabbath. For three years prior to this he had preached, as a laypreacher, the doctrines of the first-day Adventists, but had become dissatisfied. He took a public position to keep the Sabbath in October of 1852 and immediately began to proclaim his new belief. He had preached and supported himself by working, but in December 1852 he devoted himself to full-time ministry. He was ordained in 1854, and for several years conducted evangelistic work in Pennsylvania, New York State, and the Middle West. He pioneered the selling of Adventist literature in quantity when in 1854 he began selling it at 35 cents a packet at one of his tent meetings in Michigan. After a brief period of discouragement in 1856 because of financial straits, he returned with great zeal to his work, although for some time he still labored under difficult circumstances.

As the result of a serious illness brought on by overwork (1865), he became deeply interested in health reform and wrote a book called Hand Book of Health; or a Brief Treatise on Physiology and Hygiene (1868).

In 1868 with D. T. Bourdeau, he pioneered Seventh-day Adventist work in California, and by 1871 had helped establish five churches in Sonoma County, one of them in Santa Rosa, where the first Seventh-day Adventist church building west of the Rockies was erected in 1869. He baptized the first three SDA members in Nevada in 1878.

The same year (1878) he was sent by the General Conference to open SDA work in England, although the field had been prepared previously by the work of William Ings, a colporteur. Loughborough's five years in England resulted in the baptism of 37 persons and the establishing of a church in Southampton.

After his return to America (1883), he traveled as a representative of the General Conference in the North Pacific region, visiting camp meetings and strengthening members who had become confused because of apostate movements.

He was president of the Michigan Conference (1865-1868), treasurer of the General Conference (1868-1869), and for six years (1890-1896) was superintendent of several General Conference districts. He was also first president of the California Conference (1873-1878; again, 1887-1890), and of the Nevada Association (1878), the Upper Columbia Conference (1884-1885), and the Illinois Conference (1891-1895).

In 1892 he published The Rise and Progress of Seventh-day Adventists, the first denominational history (revised in 1905 as The Great Second Advent Movement). He published a number of other books, among them The Church, Its Organization, Order, and Discipline (1907), which for many years served in place of the church manual, and wrote many articles for denominational papers and edited the Pacific Health Journal for a time.

Loughborough made a world tour in 1908, including Europe, Africa, Australia, and New Zealand in his itinerary, which closed his active service, with the exception of occasional preaching at camp meetings and attendance at General Conference sessions.