[2] In the early 1950s he began performing in local music revues in Pittsburgh, and was also seen occasionally as a featured singer on the KDKA-TV program The Bill Brant Show.
[4] In 1962 Mosley relocated to New York City to pursue further studies in singing after winning the John Jay Whitney Foundation prize which provided him with funds for professional vocal training.
[7] In 1969 he was heard with the NYCO again as Tonio in Pagliacci and he toured the United States in performances of Carl Orff's Carmina Burana with the American Symphony Orchestra and conductor Leopold Stokowski.
[8] In 1971 Mosley made his debut at the San Francisco Opera (SFO) in the title role of Giuseppe Verdi's Rigoletto with Carol Toscano as Gilda and Harry Danner as the Duke of Mantua.
He notably created the role of Leonce in the world premiere of William Grant Still's A Bayou Legend Opera/South in Jackson, Mississippi on April 10, 1976.
[10] In 1976 Mosley made his debut at the Houston Grand Opera (HGO) as Porgy to Clamma Dale's Bess in the company's landmark production of that work.
On February 23, 1985 Mosley made his debut at the Metropolitan Opera as Porgy to Grace Bumbry's Bess with James Levine conducting.