Eugene D. Engley (April 5, 1851 – April 18, 1910) was an American attorney and political activist. Engley is best remembered as the 9th attorney general of the state of Colorado, holding that position as the elected candidate of the People's Party from 1893 to 1894. Engley was also a prominent figure in the Colorado Labor Wars of 1903–04 as an advocate for the striking miners affiliated with the Western Federation of Miners.

Eugene D. Engley was born April 5, 1851, in Attleborough, Massachusetts, the son of James Henry Engley and his wife, the former Mary Kaley.

After attending public school in Massachusetts, Engley came west to Colorado in 1873, setting up residence in the southwestern corner of the state.

Engley married Hilda Jayne Gaines in Colorado Springs on April 4, 1881. His wife would die of uterine cancer in 1898, at the age of 43.

Engley began his life in Colorado as a newspaper publisher, launching the first newspaper in La Plata County, The Southwest. Engley later moved to Durango, Colorado, where he published a newspaper called The Daily Republican. In 1882 Engley was chosen as the city attorney of Durango.

Engley moved to the town of Antonito, Colorado, where he served intermittently as county attorney of Conejos County from 1884 to 1891. Engley was made the city attorney of Antonito in 1891.

In 1892 Engley became active in the People's Party (so-called "Populists"). In 1893 Engley was elected Colorado Attorney General on the People's Party ticket, defeating both Republican and Democratic opponents. He would remain in that position until the expiration of his term of office in 1894.

As was the case with many populists following the fusion of the People's Party with the Democratic Party during the Presidential campaign of William Jennings Bryan in 1896, Engley moved into the emerging socialist movement in subsequent years. Engley was instrumental in writing the first two platforms of the Socialist Party of Colorado following the establishment of the Socialist Party of America in 1901.