[43] In Lemmon v. New York, Culver argued that, as New York law did not permit slavery, any slave arriving in New York was automatically freed.[43] The argument was successful, and after several appeals was upheld by the New York Court of Appeals in 1860.[43] Campaign biographers would later give Arthur much of the credit for the victory; in fact his role was minor, although he was certainly an active participant in the case.[44] In another civil rights case in 1854, Arthur was the lead attorney representing Elizabeth Jennings Graham after she was denied a seat on a streetcar because she was black.[44] He won the case, and the verdict led to the desegregation of the New York City streetcar lines.[44]
In 1856, Arthur courted Ellen Herndon, the daughter of William Lewis Herndon, a Virginia naval officer.[45] The two were soon engaged to be married.[46] Later that year, he started a new law partnership with a friend, Henry D. Gardiner, and traveled with him to Kansas to consider purchasing land and setting up a law practice there.