The 8th Utah Territorial Legislature comprised members of the Territorial Council serving the second year of their terms, together with members of the House of Representatives elected to one-year terms.
The legislative session convened amid some confusion on December 13, 1858. While newly installed Governor Alfred Cumming summoned the Legislative Assembly to meet in Fillmore at the Territorial Statehouse, only a minority of legislators appeared there when the session opened. It is not clear if Cumming was aware that the 1856 session of the legislature had abandoned Fillmore and relocated the capital to Salt Lake City, but on that basis a quorum of both houses initially met at the Social Hall in Salt Lake. The Salt Lake City group adjourned and traveled to Fillmore where the session resumed with the majority of the legislature on December 18. The legislators apparently were able to convince Cumming of the inadequate accommodations in Fillmore and inconvenience relative to population centers, especially as the Governor's office was also in Salt Lake. The Assembly thus passed a resolution with his approval to adjourn again and re-convene in Salt Lake City on December 27. The session then concluded as scheduled on January 21, 1859.
As the Mormon population had evacuated northern Utah settlements in the face of the Utah Expedition, the election did not entirely follow previous apportionments. Carson County did not send a representative after a disputed election, and with the US Army effectively occupying Green River County, two additional representatives were elected from Salt Lake County instead. However, when the legislature returned to Salt Lake from their detour in Fillmore, William J. Osborn, a civilian teamster attached to the expedition, presented himself with a certificate of election as the representative from Green River. The issue was resolved by having one of the representatives from Salt Lake resign (William H. Hooper), and Osborn became the first member of the territorial legislature who was not a member of The Church of Jesus Christ of Latter-day Saints.