Born in Czerniki, Ostpreußen, as Sohn eines evangelischen Pfarrers studierte Thomaschek an der Albertus-Universität Königsberg Theologie und Philologie. 1846 wurde er Mitglied der . Won for singing by Eduard Mantius in 1847, he was trained by Franz Hauser in Munich. He had his first stage appearance in 1849 in Danzig in the . It followed annually changing engagements: Hoftheater Sondershausen (1849/50), Mainfranken Theater Würzburg. (1850/51), Barfüsserkloster Zurich (1851/52), Volkstheater Rostock (1852/53), Staatstheater Kassel (1853/54), Deutsche Oper Amsterdam (1854/55), (1855/56) and Szczecin City Theatre (1856/57). With a Wanderbühne, he was in Lausanne and Chambéry in 1857/58. Then he found firm engagements in Theater Lübeck. (1858/59), at the Staatstheater Nürnberg, at the Salzburger Landestheater (1861/62) and at the Theater Basel (1862/63). After he had worked in 1864/65 at Stralsund Theatre had been a singer and director, he went even further north in 1865/66, to the new (German) Latvian National Opera. After one year at the , he went to the Theater Trier as singer and director (1867/68), the Landestheater Detmold (1868/69), the Theater Chemnitz (1869/70) and the Grand Theatre, Poznań (1870/71). After the Proclamation of the German Empire, he came to the Landestheater Altenburg. In 1873/74, he sang at the Stadttheater Freiburg in the Augustinian Monastery, Freiburg, in the following season at the Stadttheater Magdeburg. He then lived in Chemnitz where his wife Luise Schmidt (1829–1887) was a singing teacher. Thomascheck won agin an engagement at the Sondershausen (1877/78) and in Trier (1878/79). He changed into a and had his last performances in the Year of the Three Emperors. For many years, he was engaged in vocal pedagogy. He spent his 23 years as a widower in a home for needy stage artists, which Marie Seebach had donated in Weimar in her will.