Harold Farberman has conducted many of the world's leading orchestras, including the London Symphony, Royal Philharmonic, Philharmonia, BBC Symphony, English Chamber Orchestra, Bournemouth Symphony, Stockholm Philharmonic, Danish Radio Orchestra, Swedish Radio Orchestra, Hessischer Rundfunk, BRT Orchestra (Brussels), Orchestre National de Lille, RAI in Rome, Mozarteum Orchestra, Hong Kong Philharmonic, KBS (Korea), Sydney and Melbourne Symphonies (Australia), and the Puerto Rico Symphony.

Upon graduating from The Juilliard School of Music, Farberman was invited to join the Boston Symphony Orchestra as a percussionist/timpanist. At the time, he was the youngest player to ever become a full-time member of the orchestra. He resigned in 1963 to devote his energy to conducting and composing. In 1966 he was appointed principal guest conductor of the Denver Symphony Orchestra; subsequently, he became music director and conductor of the Colorado Springs Symphony and Oakland Symphony Orchestra, and principal guest conductor of the Bournemouth Sinfonietta in Great Britain.

Farberman has recorded more of Charles Ives's works than any other conductor and is the only conductor to date to have recorded all four of the composer's symphonies. As a result, he was honored with the Ives Award from the Charles Ives Society.

A prolific composer, Farberman counts orchestral works, chamber music, concertos, ballet music, film scores, song cycles, and three operas among his compositions. His opera The Losers was commissioned by The Juilliard School of Music and premiered at Lincoln Center. His chamber opera Diamond Street premiered at the Hudson Opera House in October 2009; it was commissioned by the city of Hudson, New York, for the Hudson Fulton Champlain Quadricentennial.

Farberman is also a tireless advocate on behalf of conductors. In the 1970s, while serving as a member of the American Symphony Orchestra League, he established countrywide workshops for young conductors. At the 1975 American Symphony Orchestra League Conference, he proposed the creation of an association of conductors; the following year the Conductors Guild became a reality, and Farberman served two terms as its first president. He is the founder and director of the acclaimed Conductors Institute, a summer conducting program at Bard College, where he is also a co-director of the Graduate Conducting Program of the Bard College Conservatory of Music.