Taylor and his wife first came in contact with the Latter Day Saint church in 1836 after meeting church apostle Parley P. Pratt in Toronto. Leonora was the first to join the church and she persuaded Taylor to continue his studies with Pratt. After the couple's baptism, they were active in preaching and the organization of the church in Canada. They then moved to Far West, Missouri, where Taylor was ordained an apostle on December 19, 1838. He assisted other church members as they fled frequent conflict to Commerce, Illinois (soon after renamed Nauvoo).

In 1839, Taylor and some of his fellow apostles served missions in Britain. While here, Taylor preached in Liverpool and was responsible for Mormon preaching in Ireland and the Isle of Man. He returned to Nauvoo, Illinois to serve as a city councilman, a chaplain, a colonel, a newspaper editor, and a judge advocate for the Nauvoo Legion. Taylor edited two newspapers in Nauvoo, the Times and Seasons which was the official organ of the LDS Church and on which he officially was the assistant editor under Joseph Smith, but due to Smith also being president of the Church, Taylor made most of the actual editorial decisions. He also edited the more politically concerned Nauvoo Neighbor. Taylor was also the editor of the Wasp, the predecessor of the Nauvoo Neighbor for about a year. Thus Taylor was the editor of Nauvoo's two main papaers from 1842-1846.

In 1844, Taylor was with church founder Joseph Smith, Jr., Hyrum Smith and Willard Richards in the Carthage, Illinois jail when the Smiths were killed by a mob. Taylor was severely wounded in the conflict. His life may have been spared when a ball directed towards his chest was stopped by a pocket watch which he was carrying at the time. However, recent analysis shows the watch may instead have been damaged when Taylor fell against the windowsill.

In 1846, most Latter-day Saints followed Brigham Young into territory then controlled by Mexico, while Taylor went to England to resolve problems in church leadership there. On his return, he and Pratt led more Latter-day Saints, a group of about 1500, to the Salt Lake Valley, where Young and the others had settled.

Taylor applied for United States citizenship in 1849. That same year he was appointed an associate judge in the provisional State of Deseret. He later served in the Utah territorial legislature from 1853 to 1876. Taylor was elected Speaker of the House for five consecutive sessions, beginning in 1857. In 1852, he wrote a small book, The Government of God, in which he compared and contrasted the secular and ecclesiastical political systems.

From 1868-1870 Taylor served as a probate judge of Utah County, Utah. He also served as superintendent of schools for Utah Territory beganing in 1876.

Taylor served as president of two missions of the LDS Church. In 1849, he began missionary work in France and was the first church mission president in the country. While in France, Taylor published a monthly newspaper called L'Etoile du Deseret. He also supervised missionary work in Germany, but did not himself go to any of the countries that would later form Germany.

Taylor later served as president of the Eastern States Mission, based in New York City. In this capacity he published a newspaper that presented the position of the Latter-day Saints.

While serving as mission president in France Taylor was directed by Brigham Young to prepare to establish a sugar industry in Utah. This was done under the auspices of the Deseret Manufacturing Company. He purchased sugar-making equitment in Liverpool while returning to the United States. These early attempts to make sugar in Utah proved unsuccessful.

Taylor is reported to have had a marvelous singing voice. At the request of Hyrum Smith (Joseph Smith's brother), he twice sang the song "A Poor Wayfaring Man of Grief" in Carthage Jail just before the Smiths were killed.

Taylor wrote the lyrics to several hymns, some of which are still used by the LDS Church. Taylor's hymn Joseph the Seer was sung at the 200th anniversary celebration of Joseph Smith's birth. The 1985 English-language edition of the LDS Church hymnal includes two hymns written by Taylor, "Go Ye Messengers of Glory" (#262) and "Go, Ye Messengers of Heaven" (#327).

Following Brigham Young's death in 1877, the Quorum of the Twelve Apostles governed the church, with John Taylor as the quorum's president. Taylor became the third president of the church in 1880. He chose as his counselors Joseph F. Smith and George Q. Cannon, the latter being the nephew of his wife Leonora.

As church president, Taylor oversaw the expansion of the Salt Lake community, the further organization of the church hierarchy, the establishment of Mormon colonies in Wyoming, Colorado and Arizona as well as in the Canadian province of Alberta and the Mexican state of Chihuahua, and the defense of plural marriage against increasing opposition.

Taylor also established Zion's Central Board of Trade while president of the Church, which was meant to coordinate local trade and production largely done through the local stakes on a wider basis.

In 1878, the Primary Association was founded by Aurelia Spencer Rogers in Farmington, Utah, and, for a time, the organization was placed under the general direction of Relief Society general president Eliza R. Snow. In 1880, Taylor organized the churchwide adoption of the Primary Association; he selected Louie B. Felt as its first general president. In October 1880, the Pearl of Great Price was canonized by the church. Taylor also oversaw the issuance of a new edition of the Doctrine and Covenants. During his term as president, the seventies quorums were also more fully and regularly organized.

In 1882, the United States Congress enacted the Edmunds Act, which declared polygamy to be a felony. Hundreds of Mormon men and women were arrested and imprisoned for continuing to practice plural marriage. Taylor had followed Joseph Smith's teachings on polygamy, and had at least seven wives. He is known to have fathered thirty-five children.

Taylor moved into the Gardo House alone with his sister Agnes to avoid prosecution and to avoid showing preference to any one of his families. However, by 1885 he and his counselors were forced to withdraw from public view to live in the "underground": frequently on the move to avoid arrest. During his last public sermon Taylor remarked, "I would like to obey and place myself in subjection to every law of man. What then? Am I to disobey the law of God? Has any man a right to control my conscience, or your conscience? ... No man has a right to do it".

Many viewed Mormon polygamy as religiously, socially and politically threatening. The U.S. Congress passed the Edmunds-Tucker Act in 1887, which abolished women's suffrage, forced wives to testify against their husbands, disincorporated the LDS Church, dismantled the Perpetual Emigrating Fund Company, abolished the Nauvoo Legion, and provided that LDS Church property in excess of $50,000 would be forfeited to the United States.

]]

For two and a half years, Taylor presided over the church from exile. During this time, he received the 1886 Revelation, which restated the permanence of the commandment to practice plural marriage; the validity of this revelation is rejected by the LDS Church but it is used by Mormon fundamentalists to justify the continued practice of polygamy.

Taylor died on July 25, 1887, from congestive heart failure in Kaysville, Utah. Taylor was buried at the Salt Lake City Cemetery in The Avenues, Salt Lake City, Utah. For two years after his death, the church was without a presidency. The Quorum of the Twelve Apostles, with Wilford Woodruff as president of the quorum, assumed leadership in this interim period. In the April church general conference of 1889, the First Presidency was reorganized with Wilford Woodruff as the president. Six months later, in the October general conference, Anthon H. Lund was called to fill President Woodruff's vacancy in the Quorum of the Twelve Apostles.

Taylor practiced plural marriage and was married to seven wives: Leonora Cannon, Elizabeth Kaighin, Jane Ballantyne, Mary Ann Oakley, Sophia Whitaker, Harriet Whitaker, and Margaret Young. He was the father of 34 children.

Taylor's son, John W. Taylor, continued to serve in the church and in politics and helped to shepherd Utah to statehood in 1896. John W. Taylor was ultimately excommunicated from the LDS Church for his opposition to the church's abandonment of plural marriage. His son, Samuel W. Taylor, became a writer, and the biographer of his father and grandfather.

Another son, William W. Taylor, served as one of the first presidents of the seventy and also served in the Utah territorial legislature.

Taylor's wife Margaret Young Taylor was a member of the inaugural general presidency of what is today the church's Young Women organization. Taylor's daughter Annie Taylor Hyde was a leader in the Relief Society general presidency and was the founder of Daughters of Utah Pioneers.