German architect and military engineer, one of the greatest of the late-Baroque and Rococo eras. He worked mainly in Franconia under the aegis of the Schönborn Prince-Bishops in the areas around Bamberg and Würzburg, where his brief covered responsibility for all military, religious, and secular architecture. His first significant major architectural work was on the new Residenz (Seat of the Court) at Würzburg from 1719, although Johann-Dientzenhofer, Hildebrandt, de Cotte, Boffrand, and von Welsch were all consulted about the design. Hildebrandt's influence is clear in the great central pavilion (the roof and pediments resemble his Belvedere in Vienna), the Kaisersaal (Emperor's Hall), the Chapel, and the fine Treppenhaus (stair), although Neumann seems to have finalized the designs about 1735. With its ceiling painted (1750–3) by Giovanni Battista Tiepolo (1696–1770), the stair at Würzburg is one of the most splendid of the Baroque period, comparable with Neumann's other ceremonial stairs at the St Damiansburg Palais, Bruchsal (1728–50), and Schloss Augustusburg, Brühl, near Cologne (1740–8). All three are spacious, ingenious, breathtakingly beautiful, and elegant.
Neumann's churches are many and invariably interesting. His first was the Schönborn Mortuary Chapel attached to the Romanesque Cathedral, Würzburg (1721–6), an adaptation of a building begun to designs by von Welsch. Among other ecclesiastical works were the Parish and Pilgrimage Church, Gössweinstein (1729–39), the Residenz Chapel (Hofkirche), Würzburg (1730–43), the Collegiate Church of St Paulinus, Trier (1734–54), the Pilgrimage Church of the Visitation of Mary (called the Käppele), Würzburg (1740–81), and the Parish and Mortuary Church of Sts Cecilia and Barbara, Heusenstamm, near Offenbach, Hesse (1739–56).
His celebrated Pilgrimage Church (Wallfahrtskirche) of the Assumption of Mary, Vierzehnheiligen (Fourteen Saints), Franconia (1742–72), had been started on site, but the spot where the Fourteen Helper Saints are said to have appeared was left in the middle of the nave rather than in the chancel as intended. Neumann turned this error to advantage, creating a large elliptical space around the Nothelfer (Helper in Time of Need) shrine, within a basically cruciform-basilican plan, and making the nave and chancel five overlapping ellipses, three of which had their long axes on the centre-line of the church, and two at right angles to the main axis. The transeptal arrangement consisted of one of the two ellipses at the crossing, with intersecting circles at either end. The resultant interlocking vaults have almost a Gothic flavour about them, but this is disguised by the sumptuously joyous Rococo decorations, with which Neumann had no connection whatsoever. It was Johann Jacob Michael Küchel (1703–69) who supervised (1762–3) the construction of the vaulting of the church, and contracts were signed (1763) with Franz Xaver Feichtmayr (1698–1763), Johann Michael Feichtmayr (1696–1772), and Johann Georg Üblhör (1703–63). for the stucco decorations. However, the deaths of two of these in 1763 left J. M. Feichtmayr in charge of the execution of the stucco-work, and Giuseppe Appiani (c. 1701–c. 1786) painted the frescoes. The lovely Gnadenaltar (Altar of Grace), a Rococo tour-de-force resembling a sedan-chair covered in marine encrustations and standing within an elliptical space to the west of the crossing, was designed (1762) by and made by J. M. Feichtmayr and Üblhör (it was completed in 1764). Neumann has been praised to the skies for this lovely building (notably by Pevsner), but the beauty of the interior owes much to those identified above, and the plan itself resembles Guarini's Santa Maria della Divina Providenza, Lisbon (1656–c.59), published in the latter's Architettura Civile (1737). However, Neumann may have evolved his plan by way of Dientzenhofer's churches in Prague, which he had visited in 1738.