Born in West Liberty, Ohio County, Virginia (now West Virginia). After studying at Ohio University, Ewing commenced the practice of law in Lancaster, Ohio in 1816. He was elected to the U.S. Senate in 1830 as a Whig and served a single term. He was unsuccessful in seeking a second term in 1836. Ewing served as Secretary of the Treasury from March 4, 1841–September 11, 1841, serving under Presidents William Henry Harrison and John Tyler. Ewing was later appointed to serve as the first Secretary of the Interior by President Zachary Taylor. Ewing served in the position from March 8, 1849-July 22, 1850 under Taylor and Millard Fillmore. Ewing was then appointed to the Senate to fill the vacancy created by the resignation of Thomas Corwin, and served from July 20, 1850-March 3, 1851. Ewing was unsuccessful in seeking re-election in 1851. Ewing was appointed by President Andrew Johnson to a third post as Secretary of War in 1868 following the firing of Edwin Stanton but the Senate, still outraged at Johnson's firing of Stanton - which had provoked Johnson's impeachment - refused to act on the nomination.