[1][2] Fredricks debuted with the New York City Opera on October 1, 1960 as Schaunard in La bohème, with Chester Ludgin and Norman Treigle in the cast.
He went on to perform leading baritone roles in The Consul (with Patricia Neway), Le nozze di Figaro (as Count Almaviva), The Ballad of Baby Doe (as Horace Tabor), Lizzie Borden (as Captain Jason MacFarlane, in the world premiere of Beeson's opera), Carmen (as Escamillo), Tosca (as Baron Scarpia, with Plácido Domingo), Cavalleria rusticana (as Alfio), Manon (as Lescaut, with Beverly Sills, conducted by Julius Rudel), Gianni Schicchi (title role), La traviata (as Germont), Lucia di Lammermoor (as Enrico), L'heure espagnole (as Mulateer), Roberto Devereux (as Nottingham), La cenerentola (Dandini), Il barbiere di Siviglia (as Figaro), Un ballo in maschera (as Renato), Maria Stuarda (as Talbot), Rigoletto (title role), Don Giovanni (title role, directed by Frank Corsaro), I puritani (as Sir Richard Forth), Manon Lescaut (as Lescaut), Pagliacci (as Tonio), Lucrezia Borgia (as Alfonzo d'Este), Andrea Chénier (as Gerard), Falstaff (as Ford) and Attila (as Ezio).
Fredricks made his first appearance with the Met in 1976 at Wolf Trap National Park as Don Carlo in John Dexter's production of La forza del destino.
In Canada, he sang the part of the Count de Luna in Il trovatore (Montreal), Rigoletto (Toronto and Quebec City), Scarpia in Tosca (Winnipeg) and as Demetrius in A Midsummer Night's Dream (Vancouver).
He appeared as himself in the November 5, 1971 episode titled, "Does Your Mother Know You're Out, Rigoletto", of The Odd Couple in which he sang selections from La traviata and Camelot ("If Ever I Would Leave You").