The United States Congress established the New Mexico Territory in September 1850. The territory included most of the present-day states of Arizona and New Mexico as well as part of Colorado

Congress provided funds to begin construction of a capitol building on public lands acquired by the United States from the Mexican government under the 1848 Treaty of Guadalupe Hidalgo. The proposed "State House" for the territory was begun in 1853 under the direction of the Supervising Architect for the Treasury.

The building was not completed until 1889, thirty-six years after it was begun.

The architectural style is Greek Revival. (This building looks out of place among the Pueblo Revival buildings which characterize Santa Fe, but the Pueblo Revival style was not codified until the 20th century.) The walls are built of rough stone taken from the Hyde Park region near Santa Fe. The door lintels, window frames and ornamental trim are of dressed stone quarried at Cerrillos, New Mexico.

In 1929, an addition was built on the north side of the original structure in the same architectural style.

New Mexico and Arizona were admitted to the United States in 1912, the last of the contiguous forty-eight states.

Source: Adapted from the NRHP nomination submitted in 1973.