[1][2][3] Seidman was born in Brooklyn, New York, and attended Poly Prep Country Day School.
[4] From 1938 to 1943, Seidman worked as director of research for the New York City Department of Investigation under Thomas E. Dewey and William Bernard Herlands.
In retirement, he consulted for the government, serving on President Richard Nixon's Ash Council on Executive Office Reorganization.
[5] After retiring from the civil service, Seidman worked as a professor of political science at the University of Connecticut from 1971 to 1984.
He was subsequently a senior fellow at Johns Hopkins University Center for the Study of American Government from 1987 until his death in 2002.