Johann Jacoby, a German publicist of Jewish descent, born in Konigsberg, May 1, 1805. He studied medicine at Konigsberg, Berlin, and Heidelberg, and became a distinguished physician in his native city. At the same time he came forward as a politician, and was under arrest in 1841-'3 for having keenly criticised the government in a pamphlet entitled Vier Fragen; and other publications resulted in his being sentenced in 1845 to a long term of imprisonment, but he was acquitted on appeal to a superior court. In 1848 he was prominent in the provisional parliament of Frankfort, and subsequently in the Prussian national assembly as the chief leader of the democratic party. After sitting in the second Prussian chamber during its brief existence in the early part of 1849, he succeeded the historian Raumer in the German parliament at Frankfort, soon retiring with that assembly to Stuttgart. Once more accused of treason, he surrendered himself to the authorities at Konigsberg, but was acquitted, Dec. 8, 1849. In the same year he declined a seat in the Prussian first chamber, and in 1862 one in the chamber of deputies, but occupied one in the latter in 1864-'5. His sympathy with democracy and socialism, and his opposition to monarchy as the promoter of German nationality, caused him to be arrested in 1866 for obnoxious passages in one of his electoral addresses, and for allusions in the biography of Heinrich Simon which he had published in 1865; and as he continued his agitations after the outbreak of the war with France, he was again placed for some time under arrest in 1870. The next year he declined a reelection by the radicals.
Elected a member of the imperial Reichstag in 1874, he renounced his seat, declaring in a letter to his constituents his conviction of the impossibility of transforming a military state into a popular state in a parliamentary way. His writings, some of which are medical, include Die Grundsatze der preussischen Democratic (Berlin, 1859).