Lalo was a significant composer of orchestral and chamber music at a period when French musicians were overtaken by a compulsion to write for the theater. He was the author of the popular Symphonie espagnole for violin and orchestra, a work that captivates the listener with its melodic charm and great passion. The intensely dramatic Cello Concerto in D minor, a piece that aptly uses the instrument's expressive ability, and the ballet Namouna are two of his lesser-known though no less accomplished compositions. Lalo ran away from home when he was 16 because his father did not allow him to try a career as a singer. He learned violin at the Paris Conservatoire and even took private composition lessons. Lalo composed while promoting himself as a violinist, playing and teaching. Pieces for the violin are among his early compositions, which were written in the 1840s. In the 1850s, Lalo became a leading figure in a trend in France to revive chamber music. He had already written two piano trios by the mid-1850s, demonstrating tremendous mastery of the genre. Lalo was a founding member of the Armingaud Quartet, which was formed in 1855 to support the music of Haydn, Mozart, Beethoven, Schumann, and Mendelssohn. In 1859, Lalo, the quartet's violist, and second violinist wrote a string quartet, improving his prestige as a chamber music composer. In 1865, Lalo married Julie Bernier de Maligny, a singer who went on to become one of his most famous performers.

Nonetheless, Lalo aspired to write operas, and in 1866 he began work on Fiesque, an opera based on Friedrich Schiller's play Fiesko. Although Lalo was satisfied with his opera, the Paris Opera refused to stage it. Despite this failure, Lalo's career continued to flourish. Lalo was inspired to begin writing for the orchestra after the Societe Nationale de Musique was established in 1871 with the mission of promoting the works of contemporary composers. In the 1870s, Lalo wrote a Violin Concerto in F major, the popular Symphonie espagnole, the Cello Concerto, and the Fantaisie norvégienne for violin and orchestra, among other compositions. Lalo began work on Le Roi d'Ys, an opera based on a Breton legend, in 1875. In 1881, Lalo gave his job to the Opera, thinking it was almost over. Theaters once again declined to stage Lalo's work; nevertheless, the Opera invited him to write a ballet, possibly as a way of compensating him. Centered on a tale from Casanova's Memoires, Lalo composed Namouna between 1881 and 1882, and the ballet was performed in 1883 to a less-than-appreciative crowd. Lalo, on the other hand, managed to support Le Roi d'Ys in the 1880s. In 1888, the opera was eventually premiered at the Opera-Comique, and it was a huge success. Following this late triumph, Lalo embarked on a variety of new ventures, including Neron, a pantomime that debuted in 1891. La jacquerie, a modern musical, appeared incomplete.