 He was president of Syracuse village from 1839 to 1841 and from 1846 to 1847, and was mayor of the town in 1849, 1850, 1859, and 1860.Leavenworth was a Whig member of the New York State Assembly (Onondaga Co., 3rd D.) in 1850 and 1857; and was Secretary of State of New York from 1854 to 1855.He was Chairman of the Republican State convention of 1860.