Raster was born in Zerbst, Anhalt-Dessau on May 6, 1827 to a family of aristocrats. His father, statesman Christian Raster was the Administrative Officer and close friend of the Duke of Anhalt, Leopold IV. Hermann was one of eight children, his siblings in order being Luise, Alexander, Wilhelm, Gustav, (then Hermann) Askan, Wolfgang, and Sophie. Christian insisted young Hermann learned English and had a tutor brought from England to teach him. By the time Hermann was an adult he was fluent in seven languages. He graduated from the University of Leipzig in 1846 and then the University of Berlin in 1848. In 1849 he took a job as the stenographer of the Anhalt Legislature. He was very involved with the German liberal political scene of the late 1840s and in 1848 was named Secretary of the State Assembly of Dessau. In 1851, he was forced to leave Germany or face trial for his actions.
Hermann arrived in New York City in July, 1851 and first found employment as a wood-chopper at a farm near Tioga, Pennsylvania. He left for Buffalo in the spring of 1852, accepting the position of editor for the Buffalo Demokrat. His journalistic reputation grew quickly and in February 1853, Raster was made editor of the New York Abendzeitung, the most influential German-language paper of the time. He had a wife, Emilia Berta Hahn Raster, born in 1836, and a daughter, Mathilde, with her in 1857. While living in New York, he became an active member of the Republican Party. In 1856, he became an elector in the 1856 presidential election. Raster was influential in leading the German-American switch to the Republican Party in 1856, swaying German public opinion via his pro-union, anti-slavery articles in the German press, and promoting the personal liberty cause. He was a very strong supporter of Abraham Lincoln and helped convince the German and European communities to vote Republican. His wife, Emilia, died on October 14, 1861, at the age of 25, of an unknown cause. She is interred at Evergreens Cemetery in New York. During the American Civil War, he was the primary American correspondent for the newspapers in Berlin, Bremen, Vienna, and other Central European cities, and was regarded as more effective in campaigning for the American cause in Germany than any politicians at the time. Up until 1867 he was also the Wagonmaster of the United States Custom House (New York City).
In 1867, Raster accepted the position as editor for the Illinois Staats-Zeitung in Chicago, where he remained until his death. In 1871 Hermann was given the position as Collector of Internal Revenue for the First Illinois District by President Ulysses S. Grant. In 1872, Raster resigned from the position as Collector of Internal Revenue to save more time for the paper and help campaign for Grant in the upcoming election. That same year at the National Republican Convention in Philadelphia inserted the "Raster Resolution" in its platform which greatly opposed the Temperance movement. Raster held so much influence over the German republican community he once threatened to leave the party if Prohibition was not made an issue and the resolution not passed and with him the entire German-American Republican community. During the Haymarket Affair, Raster was trying to delegate the rioters before he left the scene when he realized any hope for the situation was lost. Once the perpetrators were caught he wrote a letter to the Governor, John Peter Altgeld demanding that the prisoners be put to death.
He blamed the recent German "immigrant radicals" for the issues at hand and suggested immigration reforms be made, stating, "Unfortunately it is from the German Reich that these bloody scoundrels, these socialists, communists, and anarchists have come." Raster died on July 24, 1891 in Kudowa-Zdrój, Silesia where he had traveled in June 1890 because of his poor health. His body was brought back to the United States on board the SS Eider of the Norddeutscher Lloyd. On August 12 his funeral services were conducted at the German Press Club in Chicago, and speakers from as far away as New York and New Jersey attended. The hall was decorated with hanging crepes and his casket, made of walnut and "heavily" mounted with silver, was "literally covered in floral emblems sent by various German-American press organizations." The German American Press Club of Philadelphia sent a large anchor, and the German Club of Hoboken, New Jersey gave a laurel wreath wrapped in the colors of the 1848 revolution, which Raster was a part of, that said, "To the German Hero from the German Club." His wife Margarethe refused to leave his casket and "sobbed violently" until the group convinced her to go to her carriage. On his death, the Chicago Tribune produced an article which said, "His writings during and after the Civil War did more to create understanding and appreciation of the American situation in Germany and to float U.S. bonds in Europe than the combined efforts of all the U.S. ministers and consuls."
His daughter Mathilde (1857-unknown) and his third wife Margarethe (1848-1908) and their three children, Anna Sophie Hercz (1874-1936), Edwin Otto Raster 1871-1926) and Walther Berthold Raster (1875-1944) survived him. Hermann Raster was interned at Graceland Cemetery on August 13, 1891, where his grave remains today.
In 1891, Raster's family and friends published a novel filled with his travel papers and biography, called "Reisebriefe von Hermann Raster".
Over 3,900 of his papers, correspondence, notes, and manuscripts were donated to the Newberry Library in 1893.
On June 8, 1908 Hermann's wife Margarethe died after falling into shallow water at the North Shore Health Resort in Winnetka. She had been in the resort for nine weeks, as a result of her diagnosed Neurasthenia and Locomotor ataxia. Her attendant, Clare Ott, left her on the pier for a moment to retrieve a shawl from the building and when she returned Mrs. Raster was lying face down in the water, dead. At first, the death was thought to be a possible suicide and in order to prevent a scandal the suburban police were not notified until the attending physician wired Deputy Coroner Adolf Hoffman. Even on the wire, they refused to give the name of the deceased. Once the coroner investigated her death, he declared she died as a result of an attack of dizziness that forced her to fall into the water, from which she could not get up. Her son, Edwin, however, is quoted as having a different opinion, stating, "As a matter of private opinion I think she was not drowned, but died of heart disease. We thought she was getting better, and she was given up until the last day the best of care by the people here."
In 1893 the Hermann Raster School was opened on 6937 Wood St in Chicago and had 200 students. In 1910, the larger Hermann Raster Elementary School was built at 6936 Hermitage Ave, but the school has since changed names and hands, and is now the Barbara Sizemore campus of the Betty Shabazz International Charter School.