His professional debut took place in 1993 as Guglielmo in Così fan tutte. Having sung a large number of baritone parts he made his transition to tenor in 2004, debuting as Laca in Jenůfa.

In addition to regular appearances at the Royal Opera in Stockholm, Weinius has performed in many European opera houses such as Opéra Bastille in Paris, Bayerische Staatsoper in Munich, Grand Théâtre in Geneva, Oper Leipzig, Den Norske Opera in Oslo, and Deutsche Oper in Berlin.

In 2018, he made his role debuts as Siegfried in Siegfried and Götterdämmerung in Deutsche Oper am Rhein’s production of Der Ring des Nibelungen, which would become signature parts in his repertoire alongside Siegmund, Parsifal, Lohengrin, and Tristan.
Other notable roles include Herod (Salome), Bacchus (Ariadne auf Naxos), Samson (Samson et Dalila), Mao (Nixon in China), Don José (Carmen), and the title roles in Peter Grimes and Otello.

After a successful debut at Wiener Staatsoper as Lohengrin, Weinius returned in 2022 to sing Siegfried in Sven-Eric Bechtolf’s production of Der Ring des Nibelungen. He completed the 2021/22 season portraying Tristan at Opernhaus Zürich.

Current engagements include Bacchus at the Royal Opera in Stockholm and Herod in Tokyo as well as Tristan in Peter Sellars and Bill Viola’s celebrated production of Tristan und Isolde in Los Angeles under the baton of Gustavo Dudamel.

Michael Weinius appears regularly on the concert stage, performing in such works as Schoenberg’s Gurre-Lieder, Beethoven’s Symphony No. 9, Mahler's Das Lied von der Erde, and Elgar’s The Dream of Gerontius.

He has collaborated with distinguished conductors such as Esa-Pekka Salonen, Kent Nagano, Axel Kober, Gianandrea Noseda, Christoph Eschenbach, Marek Janowski, Gustavo Dudamel, Donald Runnicles, and Christian Thielemann.