Snow was with the vanguard company of Mormon pioneers led by Brigham Young. On 21 July 1847 Snow and Orson Pratt, alternately riding a single horse and walking, followed the Donner Party trail over Little Mountain and down Emigration Canyon, and they were the first of the Mormon pioneers to enter Salt Lake Valley.
Snow participated in the organization of the State of Desert in 1849, and, representing southern Utah, was a member of the Utah territorial legislature.
He was a colonizer in Utah, New Mexico, Colorado, and Arizona; and he established southern settlements on the Virgin and Santa Clara rivers for the purpose of raising cotton. With George A. Smith, Snow organized the Deseret Iron Company in Iron County, and founded St. George in 1861. Snow was an outstanding leader and directed the settlements in southern Utah for many years. Sanpete Academy was renamed Snow College in 1902 in honor of Erastus Snow and LDS Church president Lorenzo Snow.
Snow served as a member of the LDS Church's Quorum of Twelve Apostles from 1849 until his death in 1888. He was known as a skilled orator, debater, and student of the Bible. He served as a missionary for much of his adult life and opened the Scandinavian Mission in 1850. While presiding over missions in the eastern states (1860-51) and Midwest (1854-56), he also supervised emigration to Utah. Several tracts, pamphlets, and newspapers were published under his direction. He supervised the publication of the Book of Mormon in Danish, which was the first foreign language edition of that book.
A polygamist like most of the early apostles, Snow had at least four wives and thirty-six children. He spent time in Mexico to protest and evade federal laws regarding plural marriage. Erastus Snow died in Salt Lake City on 27 May 1888.