Herman Cornejo began his ballet studies at the age of eight at the Superior Institute of Art at the Colon Theater. A multiple prize winner in several prestigious South American competitions, he went on to study at the School of American Ballet in New York as a scholarship student. He then joined Ballet Argentino in 1995.

At the age of 16, Mr. Cornejo became the youngest Gold Medal winner in the history of the VIII International Dance Competition in Moscow (1997). He was then promoted to Principal Dancer with Ballet Argentino, alternating with Julio Bocca in all the principal roles in the repertoire during the company's worldwide tours.

Mr. Cornejo joined American Ballet Theatre in 1999 and was promoted to Soloist in August 2000, and was appointed Principal Dancer in August 2003. His roles with ABT and as a guest artist with others companys, include, Basilio in Don Quixote, Romeo and Mercutio in Romeo & Juliet, Franz in Coppelia, Siegfried in Swan Lake, Ali, Birbanto and Lankedem in Le Corsaire, Prince Desire in Sleeping Beauty, Lescaut in Manon, Albrech in Giselle, James in La Sylphide, Hortensio in The Taming of the Shrew, Puck in Frederic Ashton's The Dream, Alain in La Fille Mal Gardee, 1st Sailor in Jerome Robbis's Fancy Free, G. Balanchine's Theme and Variations, Symphony in C, Tarantela, The Suite of Who Cares?, Tchaikovsky Pas de Deux, Le Spectre De La Rose and Petrouchka, Yelow Couple in Martha Graham's Diversion of Angels, Diana & Acteon Pas de Deux, Flames of Paris Pas de Deux, Christian Spuck's Le Grand Pas de Deux, Jiri Kylian's Petite Mort and Sinfonietta, William forsythe's Workwithinwork, Clark Tippet's Bruch Violin Concerto, Robert Hill's Marinba, Twyla Tharp's In The Upper Room and Sinatra Suite. He created roles in Twyla Tharp's Variations on a Theme By Haydn, Stanton Welch's Clear.

In 2000, UNESCO honored Mr. Cornejo in Argentina as a Peace Messenger, and he was granted a Special Distinction by the Argentinian Embassy in Washington, DC.