Isaac Peckham Christiancy (March 12, 1812 – September 8, 1890) was chief justice of the Michigan State Supreme Court and U.S.

In 1836, Christiancy was admitted to the bar after moving to Monroe, Michigan, where he obtained a clerkship in a Federal land office.

He was a member of the Michigan State Senate from 1850 to 1852 and an unsuccessful Free Soil Party candidate for governor in 1852.

[1] He served as Envoy Extraordinary and Minister Plenipotentiary to Peru from 1879 to 1881, after which he returned to Lansing, Michigan to resume the practice of law.

During his stay in Peru, Christiancy warned the United States about the rising British influence that was being brought about by Chile during the War of the Pacific.

[2] Christiancy also wrote that Peru should be annexed for ten years and then admitted in the Union to provide the United States with access to the rich markets of South America.

He was awarded the Medal of Honor during the American Civil War while serving in Company D, 9th Michigan Volunteer Cavalry.