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After working for the Office of Chief Counsel for the Internal Revenue Service (Cleveland District Counsel) from 1973–78, Armen worked in the Criminal Tax Division from 1978–79, as Washington District Counsel from 1979–81, and as a law clerk to United States Tax Court Judge Howard A. Dawson, Jr. from 1981-83.
He was Assistant Clerk of the Court, 1983–85, and then became Deputy Counsel to the Chief Judge, 1986-93. He was made adjunct professor at University of Baltimore Law School (Graduate Tax Program, 1988–90), and the Northern Virginia Community College (Business Division, 1981–89). Armen was appointed as a Special Trial Judge, United States Tax Court on August 27, 1993.