In 1865 Davis was elected a member of the West Virginia House of Delegates.
The following year, he founded the Potomac and Piedmont Coal and Railway Company with the intent of furnishing transportation to his coal mining and timbering interests.
The company was given the right to construct railroad grades in Mineral, Grant, Tucker and Randolph counties.
He became a state senator in 1869.
In 1870, he was elected to the United States Senate, serving two terms, with his service ending in 1883.

Following his service in the Senate, Davis retired to Elkins, West Virginia, where he resumed banking and coal mining.
 Davis’ company now controlled 135,000 acres (550 km²), employed 1,600 men of sixteen nationalities, operated two power plants, and worked over 1,000 coke ovens and 9 mines within one mile (1.6 km) of the central office at Coketon in Tucker County.
By 1892, the Davis Coal and Coke Company, a partnership between Davis and his son-in-law, Senator Stephen Benton Elkins, was among the largest coal companies in the world.

Davis represented the U.S. at the Pan-American Conferences of 1889 and 1901.
In 1865 Davis was elected a member of the West Virginia House of Delegates. The following year, he founded the Potomac and Piedmont Coal and Railway Company with the intent of furnishing transportation to his coal mining and timbering interests. The company was given the right to construct railroad grades in Mineral, Grant, Tucker and Randolph counties. He became a state senator in 1869. In 1870, he was elected to the United States Senate, serving two terms, with his service ending in 1883.
Following his service in the Senate, Davis retired to Elkins, West Virginia, where he resumed banking and coal mining.  Davis’ company now controlled 135,000 acres (550 km²), employed 1,600 men of sixteen nationalities, operated two power plants, and worked over 1,000 coke ovens and 9 mines within one mile (1.6 km) of the central office at Coketon in Tucker County. By 1892, the Davis Coal and Coke Company, a partnership between Davis and his son-in-law, Senator Stephen Benton Elkins, was among the largest coal companies in the world.
Davis represented the U.S. at the Pan-American Conferences of 1889 and 1901.
Henry Gassaway Davis