Hardt was born in San Antonio, Texas, a son of the Rev. and Mrs. W.W. Hardt. On 13 September 1943 he married Martha Carson of Malakoff, Henderson County, Texas. They have four children: Betty (Mrs. Ed Lesko), William C., John S. and James J. (known as Joe). The Hardts also have eight grandchildren.
During college Hardt served as a supply pastor. Bishop A. Frank Smith ordained him a Deacon in 1943 and an Elder in 1944 in the TexasAnnual Conference. In 1943 Hardt relieved his father as Pastor at Malakoff. Following the death of his father, Hardt served there another year.
Hardt served four other pastorates in the Texas Conference, each one involving a major building program. In 1977, after serving the First U.M.C., Beaumont, Texas for eighteen years, he was appointed Superintendent of the Houston East District until elected to the Episcopacy in 1980. Hardt was a delegate to all U.M. General Conferences from 1960 until 1980, during which time he was also active on general and conference agencies.
Upon his election, Bishop Hardt was assigned to the OklahomaEpiscopal Area. He served Oklahoma until his retirement in 1988. He then became Bishop-in-Residence at Perkins School of Theology, later becoming Bishop-in-Residence Emeritus.