After a year traveling around the world, he entered Columbia University as a graduate student in 1934 in political science with a specialty in public administration.
On September 2, 1934, he married Catherine Letsinger of Bloomfield, Indiana, whom he had dated at DePauw and who was earning her degree in the School of Journalism at Columbia.
[citation needed] After World War II, he returned to the graduate faculty of Columbia University, rising to the rank of tenured full professor.
He became the first chancellor of the Ohio Board of Regents, 1964–1972, enjoying a close working relationship with Governor James A. Rhodes.
Millett authored or coauthored nearly two dozen books and numerous professional journal articles in educational policy and public administration.
[citation needed] Millett was a longtime affiliate of political science honors society Pi Sigma Alpha.
[citation needed] Millett retired from public service in Ohio in 1972 and joined the executive leadership team at the Academy for Educational Development in Washington, D.C.
He suffered a severe heart attack in 1988 and subsequently died after a long illness at a retirement center in Cincinnati, Ohio.