Born in Oklahoma, Mace did his undergraduate studies at the Oklahoma State University, graduating with a B.A. in history in 1973. He pursued his graduate studies at the University of Michigan, where he studied with Roman Szporluk, receiving a Ph.D degree in 1981, with a thesis on national communism in Soviet Ukraine in the 1920s. Starting in July 1981, Mace worked as a postdoctoral fellow at the Harvard Ukrainian Research Institute. Following the advice of Omeljan Pritsak, the director of the Institute, he started doing research for Robert Conquest's book on the Great Famine in Ukraine, The Harvest of Sorrow.
From 1986-90, Mace served as the executive director of the U.S. Commission on the Ukraine Famine, in Washington, D.C.. In 1993 he moved from the United States to Ukraine. Since 1995, he was a Professor of Political Science at the National University of Kyiv-Mohyla Academy.
Mace died in Kyiv, aged 52. He is survived by his wife, Natalia Dziubenko-Mace, one son from a previous marriage, William, and two adult stepchildren. The Order of Yaroslav Mudry, 2nd Class was awarded posthumously to Mace by President Viktor Yushchenko, in 2005. A monument in his memory was scheduled to be established in Kyiv in 2008.
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In his works, he argued that the famine in Soviet Ukraine during the early 1930s was an act of genocide on the part of Soviet leader Joseph Stalin. In 1982 at an international conference on the Holocaust and genocide Mace stated: "In order to centralize the power in the hands of Stalin, what was needed was to destroy the Ukrainian peasant, the Ukrainian intellectuals, the Ukrainian language, Ukrainian understanding of their history and to destroy Ukraine as such. This was simply calculated and primitive: No people, as a result no country, and the result - no problem."
As the director of the US Commission into the study of the Ukrainian Famine he collected eye-witness accounts from survivors in North America. Over 200 hours of audio recording were handed over to the Ukrainian Parliamentary Library in Kyiv. The tapes of these eyewitness accounts were found scattered over the floor of the library vandalized, some totally destroyed.