Siv Wennberg was born in Timrå, Sweden, in 1944. She received her musical education at the Ingesund College of Music (1961-63) and the Royal Swedish Academy of Music (1964-71) initially as a pianist and then also as a singer.

Her career got off to a flying start when, at the age of 28, she sang three major Wagner roles and Verdi´s Aida within a ten-month period. She made her debut at the Royal Swedish Opera in Stockholm as Sieglinde in Die Walkure in 1972, conducted by Silvio Varviso. The same year she sang Senta (The Flying Dutchman) at the Vienna State Opera and Elisabeth (Tannhäuser) in Geneva. She also sang Elisabeth at Covent Garden in London in 1975, and the Empress in Die Frau ohne Schatten in Stockholm in 1975 and 1978, the latter alongside Birgit Nilsson in a performance that was also televised. Wennberg has sung the role of Senta 135 times. She has made guest appearances in such cities as Munich, Hamburg, Berlin, Cologne, Wiesbaden, Graz, Nice, Rouen, Lyon, Marseille, Barcelona, Turin, Lisbon, Copenhagen, Moscow,(Bolshoi Theatre), Paris, Venice and Duisberg, and has had longer engagements in Stuttgart and Frankfurt. In Stuttgart she performed together with eminent representatives of the generation of German singers active in the 1950´s such as Martha Mödl, Gottlob Frick, Wolfgang Windgassen and Gustav Neidlinger. In the role of Sieglinde she sang alongside James King´s Siegmund on numerous occasions. Wennberg has also performed such roles as Leonora (Fidelio), Tosca, Desdemona (Otello), the title role in Ariadne of Naxos, Elsa (Lohengrin) and Brunnhilde (Die Walkure, Siegfrid). after making a comeback at the Royal Swedish Opera in 1984 as Lady Macbeth in Verdi´s Macbeth under Felice Cillario, she has also enjoyed great success with roles such as Amelia in Un ballo in maschera (alongside Nicolai Gedda; the performance was also televised), Salome, Senta, Elektra, and took part in the world premiere of the opera Christina by Hans Gefors. The concert performance of Wagner´s Tristan und Isolde at the Stockholm Concert Hall in 1988, with the Norrköping Symphony Orchestra conducted by Franz Welser-Möst was a milestone in her career. In operettas such as Offenbach´s Orpheus in the Underworld and Franz von Suppé´s Boccacio, Wennberg has also demonstrated her flair for comedy. In addition she has appeared frequently as a concert, church and Lieder singer.