Horowitz is best known for his performances of the romantic repertoire, with his six recordings of Rachmaninoff's Piano Concerto No. 3 and Franz Liszt's Hungarian Rhapsodies being particularly highly acclaimed. He is also famous for his transcriptions, the most extensive being the complete rewriting of the piano version of Mussorgsky's Pictures at an Exhibition and the most exciting being the impossibly difficult transcription of Liszt's Hungarian Rhapsody No. 2. Towards the end of the Friska section of this piece, Horowitz appears to have three hands as he combines all the themes of the piece resulting in a fantastic finale. He only recorded it once in 1953 for his 25th anniversary concert at Carnegie Hall and he said, "it is probably the hardest piece I have ever played." Other transcriptions of note are his Variations on a Theme from Bizet's Carmen and of course, Sousa's Stars and Stripes Forever. Audiences would not let him leave the concert hall until he played his "scoring" of this piece. Later in life, he abstained from playing it altogether, as he said "the audience would forget the concert and only remember Stars and Stripes, you know." Other well-known recordings include works by Schumann, Scriabin, Chopin and Schubert. He did much to champion contemporary Russian music, giving the American premieres of Sergei Prokofiev's 6th, 7th and 8th piano sonatas. He also premiered Samuel Barber's Piano Sonata.

He was sometimes accused of self indulgence in his performances, but his extravagances were always well received by his audiences. Indeed, there are "bravo!"s in all his recorded live performances. He is most famous for his octave technique; his scales in octaves move so rapidly his hands appear a blur. He had an unusual technique, playing with very straight fingers and low wrists. The little finger of his right hand was always curled tight until it needed to play a note, and as Harold Schonberg rightly put it, "it was like a strike of a cobra".