Kniplová possessed a large voice with a sonorous, metallic, dark timbre that was particularly well suited to the dramatic soprano repertoire.

While she was most admired in Czech operas and as Wagnerian heroines, she sang a wide repertoire that also encompassed Italian, Russian, and Hungarian language roles.

Born in Ostrava to a musical family, Kniplová had her first vocal training from her father before studying under Jarmila Vavrdová at the Prague Conservatory from 1947 to 1953.

Among the roles she performed there were Emilia Marty in Janáček's The Makropulos Affair, Judith in Bartók's Bluebeard's Castle, Katerina in Martinů's The Greek Passion, Kostelnička Buryjovka in Janáček's Jenůfa, Renata in Prokofiev's The Fiery Angel, and the title heroines Libuše and Shostakovich's Lady Macbeth of the Mtsensk District.

She expanded her repertoire by Anežka in The Two Widows, Brünnhilde in Wagner's Der Ring des Nibelungen, Eva in Die Meistersinger von Nürnberg, Isolde in Tristan und Isolde, Kundry in Parsifal, Lady Macbeth in Verdi's Macbeth, Leonora in Beethoven's Fidelio, Milada in Smetana's Dalibor, Senta in Wagner's Der fliegende Holländer, and the title roles in Janáček's Káťa Kabanová, Fibich's Šárka, and Puccini's Tosca and Turandot.