His father died before Mantle was born, and his mother converted to Mormonism and immigrated to the United States with her children.

Mantle attended a village school and moved to Idaho Territory in 1870, where he was a telegraph operator and stage agent for Western Union.

Mantle was publisher of the Inter Mountain until 1901 and became wealthy through investments and ownership stakes in real estate, mines, insurance, and other ventures.

[2] A convert to Mormonism, in 1864 she brought her family of four boys and three girls to the United States, and they settled in Salt Lake City.

[2][3] After deciding that the Mormon missionaries who had recruited her had not been truthful with respect to the church's practice of polygamy, the Mantles renounced their affiliation.

[2] At age 16 he obtained a job with the Union Pacific Railroad, which employed him as a teamster to haul ties and other supplies and equipment.

[2] In 1873, Mantle was assigned as a telegrapher at the Western Union office on the stagecoach line between Corinne, Utah and Helena, Montana.

[2] Mantle was the Western Union telegraph operator and postmaster, and also purchased an interest in a toll road through Monida Pass.

[2] In 1877, Mantle sold his Haskell Pass businesses and moved to Butte, Montana, where he was employed as telegrapher by Wells Fargo & Company and also started the city's first insurance brokerage.

[2] Through the paper's editorial stance, Mantle became a Republican leader and largely shaped the party's organization and policies in Montana.

[2] When Montana was admitted to the Union in 1890, Mantle was a candidate for the U.S. Senate, and narrowly lost in the legislature's Republican caucus to Wilbur F. Sanders and Thomas C. Power, who were elected.

[2] Also in 1893, Mantle was named chairman of the state commission that organized Montana's participation at the World's Columbian Exposition in Chicago.

[2] In the Senate, Mantle served on the Finance Committee, where he worked to obtain passage of amendments to the Dingley Act tariff which were favored by the National Wool Growers Association.

[6] Mantle was also an advocate of the Free silver movement, which many Montana miners favored in the belief that it would make their holdings more valuable.

[1]: 121–122  In 1897, outgoing President Grover Cleveland withdrew six million acres of forest land from the public domain to be set aside as a timber reserve.

[2] He was a noted civic activist, and his memberships included the Masons, Elks, Knights of Pythias, and the Rocky Mountain Club of New York City.

[1]: 158–159  Mantle was a major candidate for the other, but after the legislature was deadlocked for over a month, Republican legislators decided to back Thomas H. Carter, who lost to Democrat Paris Gibson.

[2] The commission chose Mantle to serve as its president, and he was responsible for creation and management of Montana's exhibits at both events.