In November1943, he made his debut as a conductor when Bruno Walter was ill, and was an immediate success. In 1949, he conducted the world première of the Turangalila-symphonie by Olivier Messaien . In 1957, he conducted the inaugural concert of the Mann Auditorium in Tel Aviv; he subsequently made many recordings there. During the 1960s, he became a well-known figure in the US through his series of "Young People's Concerts" for US public television.
On Christmas Day, December 25, 1989, Bernstein conducted Beethoven's Symphony No. 9 as part of a celebration of the fall of the Berlin Wall. The concert was broadcast live in more than twenty countries to an estimated audience of 100 million people. For the occasion, Bernstein reworded Friedrich Schiller's text of Ode to Joy, substituting the word "freedom" (Freiheit) for "joy" (Freude). "I'm sure that Beethoven would have given us his blessing", said Bernstein.
Bernstein was a highly-regarded conductor among many musicians, in particular the members of the Vienna Philharmonic Orchestra and the Israel Philharmonic Orchestra, of which he was a regular guest conductor. He was considered especially good in the works of Mahler, Copland, Johannes Brahms, Dmitri Shostakovich and of course his own. However, some people found his conducting style to be histrionic, irritating and distracting; he danced and went into fits of exultation as he conducted. Bernstein's personal life was marked by anguish over the trade-off between a conductor's glory and a composer's productivity, and the criticism invited by his impassioned political activism. It has been alleged that Bernstein also felt a conflict between his devotion to his family and his bisexuality, but Arthur Laurents (Bernstein's collaborator in West Side Story), told Charles Kaiser (author of The Gay Metropolis) that Bernstein was simply "a gay man who got married. He wasn't conflicted about it at all. He was just gay." Another friend of Bernstein, Shelly Rhoades Perle, told Bernstein's biographer, Meryl Secrest, that she thought "he required men sexually and women emotionally."
Bernstein suffered bouts of depression in his later years.
Bernstein married Felicia Montealegre, a Chilean, in 1951 and with her had three children. Although a loving father, Bernstein was notorious in the musical world for his promiscuity. The couple separated in the mid-1970s when she discovered that Bernstein had had several homosexual relationships. After the separation with his wife, Bernstein lived with Tom Cochran, his partner since 1971. He returned to care for his wife when she became terminally ill.