Born in New Orleans, Pilié was educated at Janin’s College on St. Louis Street. He was employed by his father Joseph Pilié, a surveyor in both the First and Second Municipalities (which became the Second and First Municipal Districts, respectively, in 1852). In 1843 Louis was appointed assistant surveyor to his father in the First Municipality. Joseph Pilié retired due to poor health the following year. Louis was elected surveyor of the First Municipality in 1846, becoming surveyor of the consolidated municipality of New Orleans in 1856. He held this position until 1867, when he was dismissed by General Philip Sheridan of the Reconstruction government because of his opposition to the use of Nicholson Patented Paving, a system using wooden blocks. During the war, Pilié had been removed from office and temporarily jailed by another Union general, Benjamin Butler.
Pilié continued the public improvements begun by his father, upgrading many streets during his terms. In 1851 he designed and supervised the construction of the iron fence that currently surrounds Jackson Square. Pilié also supervised the renovation of the square, which involved the planting of grass, trees, and shrubs, the introduction of marble statues of the Four Seasons, the removal of the sycamores, and the relocation of the fountain. Additionally, he designed the iron gates at the Cabildo, which were installed around 1851. Due to the rapid growth of the city in the first half of the nineteenth century, Pilié proposed that the old faubourg squares be renumbered and the city streets be systematically extended across surrounding vacant tracts to guide future subdividers. However, the work was not carried out due to the Civil War. He returned to private practice, and served as an assistant city surveyor later in his life. Pilié passed away at the age of 66.