In 1855, he participated in the nationally covered rescue of Jane Johnson, a slave who sought help from the Society in gaining freedom while passing through Philadelphia with her master John Hill Wheeler, newly appointed US Minister to Nicaragua. Still and others liberated her and her two sons under Pennsylvania law, which held that slaves brought to the free state voluntarily by a slaveholder could choose freedom. Her master sued him and five other African Americans for assault and kidnapping in a high-profile case in August 1855. Jane Johnson returned to Philadelphia from New York and testified in court as to her independence in choosing freedom, winning an acquittal for Still and four others, and reduced sentences for the last two men.