His father was a lay preacher, and the young Vickers often sang for services. As his vocal gifts became more and more evident, he began to reconsider his aspirations for a career in business; his inclination towards music was confirmed in 1950, when he received a Royal Conservatory scholarship to study voice in Toronto. There he learned technique (founded in Baroque rather than Wagnerian music) from George Lambert and interpretation from Herman Geiger-Torel. He made his operatic debut as the Duke in Rigoletto at the Toronto Opera in 1954, and continued to sing in local houses and for Canadian radio in a wide variety of roles, from Ferrando in Così fan tutte to Alfredo in La Traviata to a few excerpts from Die Walküre and Parsifal.
In 1956, frustrated with what appeared to be a limited career and unsure whether he wanted the pressures of an operatic lifestyle, he was considering leaving music, but within a month of the deadline he gave himself to decide, Covent Garden invited him to make his debut as Riccardo in Un ballo in maschera in 1957. Other roles and debuts quickly followed: his Bayreuth debut as Siegmund in 1958, his Vienna State Opera debut in 1959 in the same role, his Met debut as Canio in 1960, and his La Scala debut the same year as Florestan in Fidelio. His first Peter Grimes was at the Met in 1967. By that time, he was one of the world's major heldentenors, and in 1969 he was made a Companion of the Order of Canada. He made his Salzburg Festival debut the next year, as Verdi's Otello (a role he filmed with von Karajan). In 1976, he took on the title role of Handel's Samson at the work's United States premiere in Dallas, and followed that with performances in other major U.S. houses. He retired in 1988.
Vickers was known for having a prickly temperament, and was famous for once interrupting the last act of Tristan und Isolde to shout at the audience, "Stop your damned coughing!" In other ways, he was deeply modest -- he refused to call himself an "artist," insisting that he was merely the interpreter of the real artists, the composers, and refused to make recital pieces or recordings of arias outside of the context of the complete work, saying that this practice inappropriately elevated the performer above the music.
His Peter Grimes is one of the most memorable renditions of the role (despite the fact that Britten found the thought of Vickers singing it so far from the original spirit that he refused to attend his performances or hear the recording), and his Tristan und Isolde is magnificent, with one of the most moving death scenes on record. In the Italian repertoire, he made a powerful Radames on the Solti recording with Leontyne Price.