He established several churches and schools, and was Kahu (shepherd) of Kawaiahaʻo Church after the departure of Hiram Bingham I. Kamehameha III appointed him Minister of Public Instruction, and his accomplishments established an educational system that earned him the nickname "The father of American education in Hawaii".

The elder Armstrong had been born in Enniskillen, County Fermanagh, Northern Ireland, and in 1786 emigrated to the United States, where he married Eleanor.

He was educated at Milton Academy, in Massachusetts, and at Dickinson College, in Pennsylvania, and graduated from Princeton Theological Seminary in 1831.

[1] Princeton president Archibald Alexander provided a letter of recommendation In 1831, when Armstrong made the decision to join the next contingent of missionaries being sent to Hawaii by the American Board of Commissioners for Foreign Missions.

He received his ordination on October 27, and Armstrong and his new bride Clarissa Chapman departed with the other missionaries aboard the Averick on November 26.

The board sent the Armstrongs to minister to cannibalistic tribes on Nuku Hiva in the Marquesas Islands July 2, 1833, through May 12, 1834,[3] serving alongside two missionary couples—the Rev.

Armstrong officiated at the June 19, 1856, wedding of Emma Rooke and Alexander Liholiho in Kawaiahaʻo Church.

Land grants were implemented for additional and improved facilities, and the kingdom began issuing its own textbooks.

The public school system accommodated the majority of the students, but Armstrong also chartered private educational institutions.