Lapostolet made his debut at the Paris Salon in 1848, aged just twenty-four, and exhibited there regularly until 1882. His works were noted for their fine execution and delicate atmosphere. In 1870, he won a medal at the Salon, followed by another distinction in 1882, consecrating his career.

He also exhibited at the Royal Academy in London in 1872, demonstrating his recognition beyond France's borders.

As a young man, Charles Lapostolet discovered Normandy, a region in full artistic bloom at the time. There, he met Eugène Boudin, becoming his friend and work companion. This meeting was decisive: Boudin passed on to him a taste for painting from the motif, for changing light, and for direct observation of nature. Together, they painted the shifting skies and seascapes of Honfleur, Le Havre and Trouville, places where the Impressionist revolution was already taking shape.

Lapostolet was also influenced by 17thᵉ century Dutch painting, particularly Jacob van Ruisdael and Jan van Goyen, masters of sky and water. From this tradition, he retains the horizontal structure of his compositions - a line of water, a strip of land, a vast sky - as well as a taste for reflections and natural chiaroscuro.