Among others, he has been accompanied on stage by Jan A. P. Kaczmarek (Oscar winner for the “Best Original Score in 2005), Steve Potts, Carlos Alberto Augusto, Paleka and Maria João.
He worked for many years with Portuguese vocalist Maria João - a cooperation that established him on the international scene.
He is mostly recognized for his recurrent collaborations with fellow Portuguese jazz singer Maria João, with whom he recorded over a dozen discs and toured Portugal and Europe several times.
The most famous performances in the festival's history include Chick Corea, Charlie Mariano, Joe Zawinul, Billy Cobham, Stéphane Grappelli, Ron Carter, Chris Potter, Jean-Luc Ponty, Ahmad Jamal, Gonzalo Rubalcaba, Joachim Kühn, Sheila Jordan with Cameron Brown, Philip Catherine, Maria João, Candy Dulfer, Barbara Dennerlein, Daniel Humair, and others more.
Rainer Maria Rilke | Carl Maria von Weber | Santa Maria | Maria Callas | Santa Maria Capua Vetere | Maria | Maria Theresa | Henrietta Maria of France | José María Aznar | Maria Muldaur | Maria Bethânia | Carlo Maria Giulini | Basilica di Santa Maria Maggiore | Ave Maria | Santa Maria, Bulacan | Maria Theresa of Austria | Maria Edgeworth | João Gilberto | Maria Montessori | María Conchita Alonso | João Pessoa | João Bosco | Erich Maria Remarque | Maria João | Maria Cantwell | Rainer Maria Latzke | Maria McKee | Santa María la Antigua del Darién | Santa Maria degli Angeli | Santa Maria, California |
In subsequent years Muthspiel played with many notable jazz musicians, including Maria Joao, Dave Liebman, Peter Erskine, Paul Motian, Bob Berg, Gary Peacock, Don Alias, Gary Burton, Larry Grenadier and John Patitucci.
Maria da Glória O'Neill (Lisbon, Mercês, 1 September 1828 - 21 June 1884), married Lisbon, Encarnação, 9 September 1848 her first cousin João de Sampaio de Roure (Hampstead, London, 16 January 1822 - 12 October 1880), son of João Pedro de Roure and wife Maria João O'Neill, and had issue
He married his girlfriend Maria João on 15 June 2007, at a farm in Ericeira.