The church measures in length, of which the nave accounts for . The nave is wide and its walls reach a maximum height of . The church's roof is unusually steep, with a
roof pitch of 63 degrees. It rises to a crown that is high. The tower is in height.
Works of art The church features a number of works of art, including a baptismal font (1614–1615) made by Franz Döteber and Portraits show the
Stadtsuperintendent of Leipzig, the oldest dating from 1614. A crucifix made by Caspar Friedrich Löbelt is one of the few remaining pieces from the times of Bach. The church also contains a number of notable epitaphs, such as the one for the knight Harras (d. 1451) and for councilor Daniel Leicher (1612). The colored windows in the choir were added after 1889. They show a number of historic motifs: a memorial to the fallen of World War I, King
Gustavus Adolphus of Sweden, Johann Sebastian Bach, Martin Luther with Elector
Friedrich der Weise and
Philip Melanchthon as well as Emperor
Wilhelm I. Between 1934 and 1940, in the working time from
Günther Ramin, 16 romantic stops were changed against neo-baroque stops. The German organ builder Christian Scheffler reconstructed and repaired the Sauer-organ in two phases: 1988 to 1993 and in the years to 2005. He restored the organ in the situation in 1908.
Alexander-Schuke-organ (1967 to 1999) Since the Sauer-Organ was considered unsuitable for Bach's music, a second organ with three manuals, 47 stops, a neo-baroque stoplist and mechanical key and stop action was built in 1966–1967 (by the Schuke company later named
Alexander Schuke Potsdam Orgelbau). It was dismantled in May 1999 for the new Woehl-Organ. 42 stops and other parts from the Schuke-organ in St. Thomas was reused in the 68 stop-Schuke-organ, built in 2000 to 2005 in
Fürstenwalde Cathedral.
Woehl-organ (since 2000) The Schuke-organ was later replaced by a new organ, built by
Gerald Woehl's organ-building company from 1999 to 2000. This "Bach organ" was designed to look similar to the Johann-Scheibe-organ, on which Bach had played in the Paulinerkirche, the stoplist is inspired by the Stertzing-organ, designed by
Johann Christoph Bach in
St. Georg's Church in
Eisenach during J. S. Bach's childhood.
Church bells The two bell chambers of the tower hold eight bells with a total weight of . The largest and most precious bell is the Gloriosa, made in 1477 by Theodericus Reinhard; it is rung only on solemnities. Their weight is , the tone an a0. Its famous incised drawings were created by Nikolaus Eisenberg. The second bell, Mittelglocke (midbell), was cast in 1574 by Wolf Hilliger, and the so-called Mönchs- oder Beichtglocke (monk's or confessional bell) founded in 1634 by Jakob König, which also strikes the hours. The smallest of the historical bells is the Gebetsglocke (prayer's bell), a work by the master Christophorus Gros from 1585. A clock bell in the lantern of the tower strikes the quarters. In 2020/21 the aforementioned bells were refurbished. Also four new bells were created in the Bachert bell foundry with inscriptions that reflect words from the motets by Johann Sebastian Bach. On Reformation Day 2021, all eight bells rang out together for the first time. ==Choir==