George Michael Decker Hahn (November 24, 1830 – March 15, 1886), was an attorney, politician, publisher and planter in New Orleans, Louisiana. He served twice in Congress during two widely separated periods, elected first as a Unionist to the U.S. House of Representatives in 1862, as a Republican to the U.S. Senate in 1865, and later as a Republican to the U.S. House of Representatives in 1884. He was elected as the 19th Governor of Louisiana, serving from 1864 to 1865 during the American Civil War, when the state was occupied by Union troops. He was the first German-born governor in the United States, and is also claimed as the first ethnic Jewish governor. By that time, he was a practicing Episcopalian.

In 1865, Hahn was elected to the U.S. Senate, but Radical Republicans refused to allow him or other senators-elect from former Confederate states to be seated. Later, he was elected for several terms as a Republican to the state House during the Reconstruction era, where he was also elected as Speaker. Hahn was active as a publisher and editor, owning and operating three newspapers in succession that supported the Republican Party, its program, and its candidates in the state. He spent much of his wealth in supporting these papers. Hahn continued to be politically active, being elected to Congress from Louisiana's 2nd congressional district in 1884 with a strong majority. He served about a year before his death in office.

Hahn was born in 1830 as the last child in his family, in Klingenmünster, Palatinate, then part of the Kingdom of Bavaria, now of Rhineland-Palatinate, Germany. His father died before he was born. Some sources indicate that Hahn's parents were Jewish.

With his widowed mother and four older siblings, Hahn immigrated as a child to the United States, arriving in New York City. The family traveled to the Republic of Texas, before settling in New Orleans in 1840. The following year, Hahn's mother died of yellow fever and the children were orphaned. With the help of his older siblings, Hahn continued his education and graduated from City High School. In 1849, at the age of 19, he began reading law under Christian Roselius, a prominent Whig attorney and later Attorney General of Louisiana. In 1851, Hahn graduated from the University of Louisiana (Tulane University) with a law degree. He worked in Roselius's office after getting his degree.

The following year Hahn was elected to the New Orleans city school board at the age of 22; he ran the school system as its director. He joined the Democratic party faction led by Pierre Soulé. In the Presidential Election of 1860, Hahn supported Stephen Douglas. He was fluent in English, French and German.

In 1860, Hahn opposed secession, delivering a pro-Union speech in Lafayette Square. He avoided taking an oath of allegiance to the Confederacy. Opposed to secession and a supporter of the Union, Hahn was elected in 1862 as the U.S. representative from Louisiana's 2nd congressional district. This incorporated most of New Orleans, which had been occupied by Union forces.

Hahn was one of two Louisiana Representatives seated in the 37th Congress, which adjourned on March 4, 1863, during the Civil War. Eventually, Hahn advised that there should be no more representation from Louisiana until it was "reconstructed." During his time in Washington, Hahn met and befriended President Abraham Lincoln.

In 1864, with almost all of Louisiana under federal occupation, General Nathaniel P. Banks, the Union Military Commander of the Department of the Gulf (responsible, among other things, for civil order in occupied Louisiana), called state elections and convened a constitutional convention. Benjamin Franklin Flanders and Thomas Jefferson Durant, prominent Unionists, opposed the moderate plan called for by General Banks. Hahn purchased a pro-slavery newspaper, the New Orleans True Delta, and used it to promote moderate Unionism supporting Banks' plan, including emancipation of slaves. Hahn ran for governor with the Free-State Party and won the election with 54% or 11,411 votes. J. Q. A. Fellows, a conservative Democrat, received 26% or 2,996 votes; and Benjamin Franklin Flanders, the radical Republican, received 20% or 2,232 votes.