The Bishop William Marmion Papers comprises forty-nine five-inch boxes, documenting the forty-seven year ecclesiastical career of William H. Marmion. The Papers include booklets, church bulletins, correspondence to and from Marmion, newspaper and magazine clippings, photographs, and reports generated by the Bishop in his service to the Episcopal Church.

The Marmion Papers are divided into four series. Materials about the personal life of Marmion compose the first series, Personal Papers. This series contains photographs of the Bishop, biographical information, and newspaper clippings. Of note are a number of folders on social issues and events; examples include religion-related performances such as and . This series also has brochures and maps on the sundry locales Marmion visited as a result of his travel to church-related events.

The second series details Marmion's Early Career from 1932 until 1950. During this time Marmion served as a priest and rector in several churches in Alabama and Texas: as Priest in Charge at St. James Church in Taylor and Grace Church in Georgetown from 1932-1935, as Associate Minister of St. Mark's Church in San Antonio from 1935-1938, and as Rector of St. Mary's on the Highlands from 1938-1950. The majority of the material in this series are on issues pertaining to the Marmion's work with the church, including his work with youth. A smaller third series covers the Bishop's tenure as Rector of St. Andrew's, Wilmington, Delaware, from 1950 through May 1954, and many of the documents in this series deal with the affairs of St. Andrew's Church.

The bulk of the Marmion Papers reside in series four, Bishop of Southwestern Virginia, 1954-1979. The series is divided into four sub-series: administrative, civil rights, international affairs, and the Vietnam War. The first sub-series, Administrative files, contains general administrative files regarding the Diocese of Southwestern Virginia and Marmion's duties in the Episcopal Church. Information covers a broad range of topics, such as projects and programs undertaken by both the church and diocese, in committee reports and diocesan reports, and correspondence pertains to the day to day operations of the diocese.

The second sub-series, Civil Rights, contains brochures, correspondence, magazine articles, and newspaper articles which Marmion either collected or produced on the civil rights movement, mainly from the 1950's and 1960's. Documents relate to the controversy over the biracial conferences at Hemlock Haven, a retreat near Marion, Virginia purchased by the diocese in 1957. While Marmion maintained the view that the youth conferences should be open to members of both races, many lay members of the diocese opposed mixed race conferences for young people, and only after five years of debate did the facility open to camps attended jointly by whites and African-Americans. The Bishop's yearly files on race relations from 1954-1965 also offer firsthand insight on the civil rights movement in the United States.

The third sub-series, International Affairs, comprises correspondence and related documents detailing the Bishop's activities in overseas affairs. A large number of the folders discuss companion diocese relationships with churches in Great Britain and Ecuador, and under the umbrella of this liaison Marmion made visits to both countries. Documents in this sub-series also outline Marmion's opposition to apartheid in South Africa. Believing economic sanctions were key to forcing the South African government to end the racial discrimination of the apartheid system, in 1969 the Bishop chaired a committee to prevent the Episcopal Church from using banks which supported that country's government. Marmion's argument was persuasive, and the church agreed not to utilize banking firms who financed South Africa.

The fourth and smallest sub-series, Vietnam War, includes brochures, correspondence, magazine articles, and newspaper clippings on the war in Vietnam between 1964 and 1975. The Bishop advocated ending the conflict in Southeast Asia, and his participation in a public anti-war demonstration in Roanoke drew the ire of some of his parishioners. Called both communist and un-patriotic, Marmion nevertheless sought to influence the United States government to seek an end to military involvement in Vietnam.