He was assassinated in 1905 by one-time union member Harry Orchard, who was also a paid informant for the Cripple Creek Mine Owners' Association.

In 1890, he was elected to the Idaho House of Representatives as a fusion candidate, endorsed by both the Democratic and Populist Parties, and he served one term.

In April 1899, members of the Western Federation of Miners destroyed the company's mill at Wardner in the Silver Valley.

Nearly five years after he left office, Steunenberg was killed outside his house in Caldwell at 1602 Dearborn Street (43°39′27″N 116°40′56″W / 43.6576°N 116.6823°W / 43.6576; -116.6823) by a bomb rigged to the side gate on 16th Avenue.

[13] Orchard claimed he was hired to kill Steunenberg by leadership of the WFM, and he had been in previous jobs that resulted in at least 17 other deaths.

[15] Modern commentators have praised Darrow's closing argument, which used powerful emotional rhetoric focused on the moral superiority of the unions' position.

[18] Pettibone was defended in a separate trial by Judge Orrin N. Hilton of Denver and was also acquitted, and charges were dropped against Moyer.

[21][22] A monument to Steunenberg was dedicated in December 1927 in Boise;[23][24] the outdoor bronze statue faces the front steps of the Idaho State Capitol from across Jefferson Street.

When in 1899 organized lawlessness challenged the power of Idaho, he upheld the dignity of the state, enforced its authority and restored LAW AND ORDER within its boundaries, for which he was assassinated in 1905.