On May 20, 1989, Bishop Hying was ordained a priest for the Archdiocese of Milwaukee. His first priestly assignment was as a parochial vicar for St. Anthony Parish, Menomonee Falls, from 1989 to 1994. Fr. Hying served as a Team Member for La Sagrada Familia Parroquia in the Dominican Republic from 1994 to 1997. He returned to the United States and served as the parochial administrator of St. Peter Parish (1998), then as the parochial vicar of St. Anthony Parish, Milwaukee, from 1998 to 1999. He was then appointed the pastor of Our Lady of Good Hope Parish, Milwaukee from 1999 to 2005. In 2006, Fr. Hying served as the parochial administrator of St. Augustine Parish, Milwaukee. He served as the Dean of Formation at Saint Francis de Sales Seminary from 2005 to 2007, and was appointed the rector of St. Francis de Sales Seminary by Most Reverend Timothy Michael Dolan, Archbishop of Milwaukee, and served in that capacity from 2007 until 2011.
On May 26, 2011, Pope Benedict XVI appointed Fr. Donald Hying the Titular Bishop of Regiae and Auxiliary Bishop of the Archdiocese of Milwaukee. He was consecrated a bishop on July 20, 2011 by Most Reverend Jerome Edward Listecki, Archbishop of Milwaukee.
On November 24, 2014, His Holiness, Pope Francis, appointed Bishop Hying as the Fourth Bishop of Gary (Indiana). Bishop Hying's installation in the Diocese of Gary took place on January 6, 2015. On April 25, 2019, His Holiness, Pope Francis, appointed Most Reverend Donald J. Hying the Fifth Bishop of Madison (Wisconsin). Bishop Hying’s installation in the Diocese of Madison took place on June 25, 2019.
Bishop Hying serves as the Episcopal Liaison for the National Association of Catholic Chaplains and as Episcopal Advisor to the U.S. Society of St. Vincent de Paul. He is also a member of the United States Conference of Catholic Bishops’ Committee on Pro-Life Activities and the Committee on Catholic Education. He is a member of the Board of Directors for Catholic Relief Services and Relevant Radio.