Salminen studied first at the Sibelius Academy in Helsinki and later in both Rome (with famed pedagogue Luigi Ricci) and Düsseldorf. After joining the Finnish National Opera as a chorus member, he advanced to small roles, making his formal debut in 1966. Upon returning to Helsinki from studies abroad in 1969, Salminen was advised that the singer scheduled for King Philipp II had fallen ill and that he was being assigned the role. Thus, at age 24, Salminen was thrust into one of the most vocally and dramatically complex parts in the entire bass oeuvre.
In 1972, Salminen was engaged by the Cologne Opera, remaining with that company until 1979. During that period, he was a guest artist at Hamburg, Berlin, Stuttgart, Düsseldorf, Salzburg, Milan, Paris, and at Savonlina in his native country. In 1973, he sang the title role in Glinka's Ivan Susanin at the Wexford Festival. The following year, he made a positive impression at his Covent Garden debut as Fasolt. He began a lengthy association with Bayreuth in 1976, making his first appearance there as Hunding in the first year of Patrice Chéreau's controversial Ring. Salminen's Metropolitan Opera debut took place on January 9, 1981, when he sang King Marke. Subsequent roles there have included Osmin, Sarastro, Rocco, and his defining Hagen. While his Metropolitan career has largely confined him to roles in the German repertory, elsewhere he has sung a far more extensive list of roles, becoming an arresting, if not necessarily definitive, exponent of Verdi bass parts. Russian opera proved fruitful territory for Salminen, especially Prince Gremin (noble, restrained); Boris Godunov, first undertaken at Zurich in 1984; and the expansive Ivan Khovansky, which he sang for the first time at Hamburg in 1994. As he entered his fifties, Salminen's voice became somewhat less steady than in his younger years, but it remained an imposing, untiring instrument. At Chicago in the late winter of 2002, he undertook an exhausting schedule, alternating Gurnemanz with Sarastro on an almost nightly basis. To both roles, he brought great dignity and an even firmer adherence to legato singing than before. Well-documented on both audio and video recording, Salminen's signature roles offer a model to other aspiring basses. His Hagen, recorded first in the Eurodisc Ring under Janowski, ripened into a terrifying study of malignancy under James Levine in the Metropolitan Opera Ring. His intense Osmin under Harnoncourt's leadership remains a superlative study, bracingly sung. His Landgraf, Daland, and Hunding likewise reside near the very apex of great vocal interpretation.