Because he took part in the German revolutionary movement (1848), Jacobi was imprisoned in Berlin and Cologne during the year of his graduation in medicine (1851). In 1853 he began his medical practice in New York City and became professor of children's diseases at the New York Medical College in 1860, holding the first chair in the subject founded in the United States. He later held professorships at New York University (1865–70) and the College of Physicians and Surgeons of Columbia University (1870–1902).