He obtained through Hans Lietzmann a post researching Latin and Greek manuscripts at the Church Fathers Commission, however this came under the Prussian Academy of Sciences so in 1938 Schneemelcher was removed by the Nazi authorities due to being "politically unreliable", due to sympathies with the Confessing Church, and was forced to turn to making a living as a bookseller's assistant.
He completely revised and enlarged the older collection of Edgar Hennecke (1865–1951) to produce the Neutestamentlichen Apokryphen in deutscher Übersetzung (Tübingen 1959–1997), which was then translated into English at The New Testament Apocrypha (1991) by R. McL. Wilson. As editor he coordinated the work of dozens of scholars including Philip Vielhauer and Georg Streck. His work is today commonly referred to as the "standard edition" of the New Testament Apocrypha. In later years, Schneemelcher's co-editor was Joachim Jeremias.
- Obituary in Theologische Literaturzeitung: Volume 128 2003 "Schneemelcher konnte seine akademische Laufbahn erst nach dem Zweiten Weltkrieg fortsetzen, parallel zu einer Tätigkeit als Landpfarrer in Stöckheim bei Northeim. Er erhielt einen Lehrauftrag an der Universität Göttingen"
- Festschrift für Günther Dehn Neukirchen/ Moers 1957
- R. McL. Wilson Preface to New Testament Apocrypha Wilhelm Schneemelcher, 2003 "Preface to the English Edition - Over the past thirty years or so 'Hennecke-Schneemelcher' has become a standard tool for those working in the field of the NT Apocrypha."
- Stephen J. Patterson, James McConkey Robinson, Hans-Gebhard Bethge The fifth Gospel: the Gospel of Thomas comes of age 1998 p. 105 "The current edition of Wilhelm Schneemelcher's standard New Testament Apocrypha contains eleven Nag Hammadi tractates..."
- John Douglas Turner, Anne McGuire, The Nag Hammadi library after fifty years p. 29 Society of Biblical Literature Meeting - 1997 "The current edition of Wilhelm Schneemelcher's standard New Testament Apocrypha..."
- Christopher R. Matthews Philip, Apostle and Evangelist: configurations of a tradition 2002 "But given the high visibility of Schneemelcher's assessment in the standard edition of the New Testament Apocrypha,"
- Larry W. Hurtado Lord Jesus Christ: Devotion to Jesus in Earliest Christianity p. 427 2005 "Two standard works on early Christian extracanonical writings are Wilhelm Schneemelcher, ed., New Testament Apocrypha and..."
- Fred E. H. Schroeder 5000 years of popular culture: popular culture before printing p189 1980 "Bibliography The standard work is: Edgar Hennecke — Wilhelm Schneemelcher: New Testament Apocrypha. English Translation edited by R. McL. Wilson"
- Adelbert Denaux John and the Synoptics p. 147 1992 "revised fifth edition of the standard, German translation of these writings: Wilhelm SCHNEEMELCHER (ed.), Neutestamentliche Apokryphen in deutscher Übersetzung, 1. Band. Evangelien, Tübingen, 1987"