On 14 June 1888 Talmage married Mary May Booth, daughter of Richard Thornton and Elsie (Edge) Booth. The couple were married in the Manti LDS Temple and had four sons and four daughters. Talmage held many church and civic offices including city councilor, alderman, and justice of the peace. On 7 December 1911 he was ordained an apostle in the Church of Jesus Christ of Latter-day Saints, and from then until his death gave great service to his church.
Of this calling and of other religious duties he said: "Every call I have received to an office in the priesthood has come to me because some one was needed to fill a particular place, and was in no sense a matter of advancement or honor to myself as an individual. . . . Early in life I realized that I would have to live with myself more than with anybody else, and I have tried to so live that I would be in good company when alone."
Among his more important writings, scientific and religious, are: First Book of Nature (1888), Domestic Science (1891), The Articles of Faith (1899), The Great Salt Lake, Present and Past (1900), The Story of "Mormonism" (1907), The Great Apostasy (1909), The House of the Lord (1912), Jesus the Christ (1915), The Vitality of "Mormonism" (1919), and Sunday Night Talks (1931), first given as radio speeches. In addition to these published works, he was the author of numerous scientific papers for journals, and was a prolific writer for church papers and magazines for a period of many years. Many of his scientific works were used as university textbooks.