When their brother Joseph Smith claimed to have had his vision of God and Jesus Christ in the grove of trees near they farm, like the rest of the family, the brothers believed Joseph and defended him against persecution from the locals. They also helped him keep the golden plates he obtained that were revealed to him in a nearby hill as again locals persecuted the family and sought to steal the plates. Although not participants in the translation process of what would become the Book of Mormon, they helped in making sure it was published and bore testimony along with six others who wrote that they saw and handled the plates.
Shortly after the church was officially organized in 1830 Samuel, who grabbed a large number of copies and set forth to spread the message of restoration. His missionary service resulted in a copy of the Book of Mormon to find itself in the hands of Brigham Young, who would become the second president of the church.
Both brothers helped in the establishment of church headquarters in both Kirtland, Ohio and Far West, Missouri. While Joseph and Hyrum were illegally detained in ironically named Liberty Jail, Samuel joined others in trying to defend the church settlements in Missouri that were sieged and then raided by mobs. He was withe David Patten, whom would go down as the first Apostle to die in the service of the church, thus a martyr. Forced to flee Missouri, Samuel and his now released brothers helped form the new settlement of Nauvoo, Illinois. As the church and city prospered, mobs from Missouri and Illinois brought out false charges and again Joseph and Hyrum were in jail.
When word came that a mob was descending on Carthage Jail on the 27th of June, 1844, Samuel, on horseback, raced to the jail from Nauvoo to try to rescue his brothers and two others also in jail, John Taylor and Willard Richards. When he arrived, it was too late and was forced to flee as mob chased him out. In his escape, he became severely injured internally and succumbed to his injuries a month later. Lucy Smith would lose three of her sons in a month All three are buried in Nauvoo.
In honor of Samuel Smith's actions as the church's first missionary, a statue was placed in and dedicated at the Missionary Training Center in Provo, Utah.
One of Hyrum's sons, Joseph F. Smith and grandson Joseph Fielding Smith would become future presidents of the church, with another direct descendant, M. Russell Ballard currently serving as an Apsotle.