Peter Victor Deuster (February 13, 1831 – December 31, 1904) was a German American immigrant, newspaperman, diplomat, and Democratic politician. He represented Milwaukee, Wisconsin, in the United States House of Representatives for three terms (1879–1885) and was American consul at Krefeld, Germany, during the presidency of Grover Cleveland.

Born in Düren, Rhenish Prussia, Deuster immigrated to the United States with his parents, who settled on a farm near Milwaukee in May 1847. Deuster had pursued an academic course at a college in Düren, but left too young to graduate.

He completed his self-education in a printing office. He started a Milwaukee newspaper called the Hausfreund in 1852; it was later taken over by George Brumder's Germania Publishing. He moved to Port Washington, Wisconsin, in 1854 and edited a newspaper. He also served simultaneously as deputy postmaster, deputy clerk of the circuit court, clerk of the land office, and notary public.

He returned to Milwaukee in 1856 and edited the Milwaukee See-Bote (later Seebote), a German language Democratic daily paper, until 1860, when he became proprietor.

The See-Bote had been founded by Archbishop John Henni as an anti-radical organ, and under Deuster's leadership it took a strong stance against German radicals and radicalism, calling Carl Schurz "a political mountebank" and railing against the new Republican Party with its freethinkers and abolitionism. During the American Civil War, Deuster was widely reviled as a prominent Copperhead, as he opposed the abolitionist influence on the Lincoln administration and defended General George B. McClellan against his critics. He encouraged negrophobia in his immigrant readers, warning that emancipation and abolitionism would lead to a "Negrocracy" as free whites were forced to compete with cheaper "black cattle," and referred to the abolitionist Milwaukee Herold as part of the "German Nigger Press". Deuster and the See-Bote were widely blamed for the November 10, 1862, anti-draft riot in nearby Port Washington. The commander of the German-majority Union Army of South-east Missouri forbade the circulation of the paper in areas under his control. Abraham Lincoln, described in the See-Bote as "the most incapable of statesmen and the most irresponsible of the butchers of men", was defended only when Deuster saw him as being harried by the more radical elements within the Republican Party. Unlike some Copperhead newspaper editors, Deuster publicly mourned Lincoln's assassination, expressing a fear that it would give free rein to the Radical Republicans and unleash a policy of "retribution and revenge".

He served as a Democratic member of the Wisconsin State Assembly in 1863, succeeding fellow Democrat John M. Stowell. He was assigned to the standing committees on state affairs and federal relations. He was subject to attacks in the Assembly because of the editorial stances of the See-Bote. He was not re-elected, and was succeeded in 1864 by J.C.U. Niedermann, elected on the National Union Party ticket. At this same time, his brother Joseph Deuster was also active in Democratic politics (at various times a member of the Common Council, sheriff, and sergeant-at-arms of the State Assembly).

In 1870 Peter purchased the Chicago Daily Union.

He was elected to the Wisconsin State Senate's Sixth District (the 3rd, 4th, 5th and 8th Wards of the City of Milwaukee, and the Towns of Franklin, Greenfield, Lake, Oak Creek and Wauwatosa) in 1870, with 2178 votes to 1704 for incumbent Charles H. Larkin, a one-time War Democrat who chose to run as an independent. He was not a candidate for re-election in 1872, and was succeeded by fellow Democrat John L. Mitchell.