b. November 30, 1815, in Otsego County, New York; d. April 24, 1884, in Chicago, Illinois. b. in Otsego County, New York. In 1835, Arnold was admitted to the bar in New York, and the following year, he moved to Chicago to practice law. He formed a law partnership with Mahlon D. Ogden that lasted until 1847. In 1842, Arnold was one of four lawyers appointed by the state legislature to investigate charges of incompetence levied against state supreme court justice Thomas C. Browne. A Democrat in politics, he served in the state legislature from 1842 until 1845 and was a presidential elector for Polk in 1844. In 1843, Arnold successfully argued before the United States Supreme Court the case of Bronson v. Kinzie, in which Chief Justice Roger B. Taney decided that an Illinois state law was unconstitutional. The law held that unless the property of a judged debtor would realize two-thirds of its appraised value, it should not be sold under execution. In 1848, Arnold became involved in the Free-Soil movement and drafted a resolution of protest against the Fugitive Slave Law in October of 1850. Arnold joined the Republican party in 1856 and was elected to the state legislature. In 1860, he was elected to Congress. After the war, Arnold published The History of Abraham Lincoln and the Overthrow of Slavery in the United States, and in 1884, he wrote his Life of Abraham Lincoln.