Monika Frimmer studied at the Hochschule für Musik und Theater Hannover in Hannover. She studied further in master-classes and worked with Birgit Nilsson, Elisabeth Schwarzkopf and Jörg Demus. In 1980 she was a winner in the national competition Bundeswettbewerb Gesang Berlin.
She was a member of the ensemble of the Staatsoper Hannover as a lyric soprano from 1980 to 1993. In 1982 she appeared as Anima in a scenic production of Emilio de' Cavalieri's Rappresentazione di Anima a di Corpo in the Marktkirche, conducted by Hans-Martin Linde. She sang the part of Najade in Ariadne auf Naxos of Richard Strauss. In the opera Sly of Ermann Wolf-Ferrari, revived by the Opera Hannover, she appeared as Rosalina. Since 1993 she has worked as a free-lance singer in opera, oratorio and Lied.
In 1987, Frimmer sang in a recording of Buxtehude's Membra Jesu nostri, conducted by Ton Koopman, with Barbara Schlick, Michael Chance, Christoph Prégardien, Peter Kooy, the Knabenchor Hannover and the Amsterdam Baroque Orchestra. In the Neustädter Kirche, Hannover, she sang in choral concerts, in 1996 Ein deutsches Requiem, and in 1988 Stravinsky's Cantata and Mozart's Great Mass in C minor. In 1991, she performed there Bach's St Matthew Passion in the last concert conducted by Erhard Egidi, together with Dantes Diwiak, Anselm Richter, Ralf Popken and Joachim Gebhardt. In 1998, she recorded Bachs St Matthew Passion with the Thomanerchor and the Gewandhausorchester Leipzig, conducted by Georg Christoph Biller. She has been a soprano soloist in the cycles of Bach cantatas of both Gustav Leonhardt and Masaaki Suzuki. With Leonhardt she also recorded Bach's Easter Oratorio and Ascension Oratorio, with Suzuki Bachs Christmas Oratorio.
In 2002, she founded together with Christa Bonhoff, Dantes Diwiak and Peter Kooy a quartet Tanto Canto to sing rarely performed music a cappella, with piano or with ensemble. The quartet recorded in 2005 excerpts from the collections Augsburger Tafel-Confect (short for: Ohren-vergnügendes und Gemüth-ergötzendes Tafel-Confect, in English: Augsburg Table Confectionery, Pleasuring the Ears and Delightful to the Soul) of the composers Valentin Rathgeber and Johann Caspar Seyfert. She has collaborated regularly with the Trio di Clarone and the Ensemble Incanto. Her piano accompanist for Lieder is Liese Klahn.
- "Monika Frimmer (Soprano)". bach-cantatas.com. 2009. Retrieved 27 October 2010.
- Theaterzeitung (in German). Theater Hannover. 1982.
- "Library Search". wolfram.schneider.org. 2010. Retrieved 31 October 2010.
- Canticum sacrum / Ein Deutsches Requiem (in German). Neustädter Kirche. 16 November 1996.
- 30 Jahre Kantorei der Neustädter Hof- und Stadtkirche St. Johannis zu Hannover (in German). Neustädter Kirche. 20 November 1988.
- Passion unseres Herrn Jesu Christi nach dem Evangelisten Matthäus (in German). Neustädter Kirche. 10 March 1991.
- "Rathgeber: Tafel-confect". arkivmusic.com. 2005. Retrieved 27 October 2010.
- "Rathgeber (1682-1750) Augsburgisches Tafel-Confect". musicweb-international.com. 2006. Retrieved 31 October 2010.
- Website von Monika Frimmer Website (in German)
- Monika Frimmer on Bachwoche Ansbach (in German)
- Literature by and about Monika Frimmer in the German National Library catalogue