Being a cantor at Hódmezővásárhely in 1946 he sang as a professional singer already. He was admitted to the Academy of Music the same year where he was a student of Mrs. Györgyné Jászó in the academic years of 1947/1948 and 1950/1951. Before completing his final year of study the ensemble of Honvéd Művészegyüttes signed him on. He was a soloist of that from 1949 to 1954, since then he has been a member of the Hungarian State Opera. He owed his contract to the great aria of the Bánk bán, that he sang for the first time with the Művészegyüttes at the Hősök tere (Heroes' Square in Budapest) on 1st of May in 1950, and then in 1953 at the World Youth Union, following which he was signed on by Aladár Tóth for and indefinite period of time.
He was one of the greatest Hungarian singer talents in the years after the war. He succeeded not only by his glittering, shiny voice material owning a penetrating force, but with the empathy manifested both in the voice nuances of roles and in acting.
He was a member of the legendary Mozart-team of the Opera in the Klemperer-period – he caused a sensation from his foremost performances in that capacity.
The reviewed version of the Hunyadi László was also premiered in the season following the renewal of Bánk bán in 1953/1954; it was more coherently framed and musically closer to the original. This premiere was also an important one in the history of that theatre: as Róbert Ilosfalvy with his superb tenor voice performed the title role in the first casting. His voice was light and opened up beautifully in higher registers.
He performed more and more Rossini, Verdi and Puccini roles at the time of Lamberto Gardelli working in Budapest. He sang in the Guillaume Tell in 1962 still as a young star tenor, that was followed by La forza del destino in 1963 and Un ballo in maschera a year later. A significant portion of the Verdi- renewals of Gardelli were built on the participation of Ilosfalvy exactly (and let us add: György Melis) at that time.
From 1966 on he had a permanent contract with the Cologne Opera. From the middle of the 1960s he had a global career: he made guest appearances in the Operas of San Francisco, New York, the Covent Garden in London, Munich, Vienna and Berlin.
The heroic color of Ilosfalvy's voice – who arrived to Budapest only as a guest artist from the second half of the 1960s – culminated gradually, and become full with a new intensity for stage and emotions that was characteristic of that generation. That just gave a special penetrating force to the Puccini-renaissance just unfolded at that time, with an addition of the fact that the entire evolvement of singing-acting capacities of Erzsébet Házy, the par excellence heroine of the history of Hungarian opera performances, occurred even during that period. The meeting of the two (and the conductor Lamberto Gardelli) in the second act of the Manon Lescaut must have given the densest moments to the stage of the Hungarian opera.
The review of his key roles also demonstrates his versatility: they cover the lyric roles of Tamino and Rodolphe through the spinto of Des Grieux and Dick Johnsonon to the heroic tenor of Alvaro, Manrico and Don Jose.
According to his own views a tenor must be born. The physical body structure and laryngeal resonance are crucial heritage to the singer at all. However all these are still not efficient: this career needs a healthy nervous system that is conflict-tolerant and can bear greater loading, as well.
He is confident with his career, as he had an international one while also performing in his home country, therefore did not need to part from the theater of Pest. Several of his performances have been recorded by the greatest companies since 1966. He was awarded the Kossuth and Liszt Prizes and is a Life Member at the Hungarian Opera.