[1] He was the Chief Justice of the Colorado Territorial Supreme Court from 1866 to 1877.

[1] Following the admission of the State of Colorado to the union on August 1, 1876, Hallett was nominated by President Ulysses S. Grant on January 9, 1877, to the United States District Court for the District of Colorado, to a new seat authorized by 19 Stat.

[1] He was confirmed by the United States Senate on January 12, 1877, and received his commission the same day.

[1] Concurrent with his federal judicial service, Hallett served as a Professor of Constitutional Law and Federal Jurisprudence at the University of Colorado at Boulder beginning in 1892, until his death.

[1] Following his retirement from the federal bench, he was a real estate speculator in Denver from 1906 to 1913.