Boris Trajanov studied singing with his father Goga Trajanov in Skopje. He continued his studies with Biserka Cvejic in Belgrade and Pier Miranda Ferraro in Milano. He made his stage debut in 1986 in the operetta The Gypsy Baron. The same year followed his operatic debut as Enrico Ashton in Donizetti's Lucia di Lammermoor.
During his career of over 20 years, he sang in more than 550 theatres and opera houses in the world, appearing in more than 35 roles. He is widely regarded as one of the best interpreters of the role of Scarpia in Puccini's Tosca. His wide repertoire contains the most important roles from Verdi's operas, such as Nabucco, Conte di Luna, Rigoletto, Rodrigo Posa, Macbeth, Ezio, Renato, Iago, Don Carlo, Giorgio Germont. He appeared also as Don Pizarro in Fidelio, Guglielmo in Maria Stuarda, Escamillo in Carmen, Prince Yeletsky in The Queen of Spades, Sharpless in Madama Butterfly, Gerard in Andrea Chénier, Alfio in Cavalleria Rusticana.