While still a student at the Academy of Fine Arts in Bratislava, Lenárd was engaged as chorus master for the Bratislava Opera Chorus. For his graduation concert at the Academy, he appeared before the Slovak Philharmonic, beginning a long association with that ensemble. In 1964, Lenárd was appointed official chorus master of the Slovak National Theatre. Five years later, he was engaged as principal conductor of Bratislava's Czechoslovak Radio Symphony
. With that orchestra, he toured and recorded extensively in a relationship that was to endure for decades. Successful appearances in the Far East led to his appointment as standing guest conductor of Tokyo's Japan Shinsei Symphony Orchestra in 1978.
In 1984, another prestigious appointment placed Lenárd in the position of principal conductor of the Slovak National Theatre in Bratislava; in the new millennium, he was made general manager of the opera company. During his many years there, he has overseen the careers of such star-quality singers as tenor Peter Dvorský
, bass Sergej Kopcák, and dramatic soprano Eva Urbanová. Elsewhere, he forged a positive relationship with the Vienna Staatsoper, Naples' Teatro San Carlo, and the Houston Grand Opera. Guest appearances in many European centers, in Brazil, Canada, and other parts of the United States, contributed to the conductor's growing reputation for mastery of his resources in the opera house and on the concert stage.
Given the title of principal conductor of the Slovak Philharmonic in 1991, Lenárd has led the orchestra in both subscription concerts and in festival performances. Among the latter were acclaimed performances of Verdi
's Manzoni Requiem at the 1993 Smetanova Litomyšl Festival. In 1995, Smetana
's Vltava was hailed as outstanding and, in 1999, Lenárd won particular commendation for a performance of Honegger
's Jeanne d'Arc au bûcher.