Pettigrew's siblings included Hannah M., Alma Jane, Henrietta Adelaide, Luella Belle, Justin A., Frederick (Fred) Wallace, Elizabeth Medora, and Harlan Page.

Pettigrew and his wife, Bessie, donated land in 1886 to aid the founding and development of Granite, Iowa, in Lyon County.

Pettigrew was a strong opponent of President William McKinley's attempt to annex the Republic of Hawaii against the wish of its many native residents.

[4][5] In a congressional speech, he stated: "The American flag went up on Hawaii in dishonor; it came down in honor, and if it goes up again now it will go up in infamy and shame and this Government will join the robber nations of the world.

Pettigrew was a supporter of a bill that sought to unilaterally dissolve tribal governments so as to force them to agree to allotment of their lands.

"[6]In the Presidential Election of 1900, while still in the Senate, he was a delegate and a major figure in the national political convention of the "Fusion" wing of the Populist Party held in Sioux Falls that convened on May 9, 1900, and lasted three days.

[7] In 1917, while being interviewed by a journalist from the Argus Leader, Pettigrew offered his opinion that the First World War was a capitalist scheme intended to further enrich the wealthy, and he urged young men to evade the draft.

The local United States Attorney secured a felony indictment of Pettigrew for suspicion of violating the Espionage Act of 1917, the same charge for which Socialist leader Eugene V. Debs was then presently serving a ten-year Federal prison sentence.

Pettigrew assembled a high-powered legal defense team headed up by his close personal friend, prominent attorney Clarence Darrow.