Frantz Charlet was a student at the Academy of Fine Arts in Brussels from 1872 to 1873 and from 1876 to 1881. His principal teacher there was Jean Portaels. Fellow students included Eugène Broerman, François-Joseph Halkett, Théo Van Rysselberghe and Rodolphe Wytsman.

He then went on to perfect his studies in Paris with renowned artists such as Jean-Léon Gérôme, Jules Joseph Lefebvre and Emile Carolus-Duran at the École des Beaux Arts. In Brussels, Charlet was a member of the artists' group "L'Essor"

Charlet was an avid traveler. Together with Théo Van Rysselberghe, Constantin Meunier and Darío de Regoyos, he made a study trip to Spain (end of year 1882 - spring 1883). After visiting the Prado in Madrid, they moved to Seville, where they met Constantin Meunier, who was working on a copy of a Descent from the Cross. Alfred Cluysenaer joined the small group and together they traveled to Tangerand then onMorocco in. They left Africa at the end of February 1883 (as appears from a letter from Charlet to Guillaume Van Strydonck). At the subsequent exhibition in Brussels, Van Rysselberghe's Orientalist works clearly received more critical attention than the entries by Charlet and De Regoyos.
In the summer of 1883 he left, again together with Théo Van Rysselberghe, for Haarlem, where they studied works by Frans Hals . He also stayed with the artists' colony in  Knokke, together with Van Rysselberghe, De Regoyos and other artist friends such as Willy Schlobach, Willy Finch and Rodolphe Wytsman. In 1883, together with Théo Van Rysselberghe and Willy Schlobach, he was at the basis of the split of "L'Essor", something that would lead to the foundation of "Les XX" in the same year. However, he did not exhibit at the first exhibition of this artists' collective, because he, together with Van Rysselberghe, had left for Tangier again, with a detour via Italy. In 1885 he visited Volendam and the island of Marken with James McNeill Whistler. He also visited the then fashionable Zealand, Switzerland, Germany, Italy and Algeria.

During a group exhibition at the Cercle Artistique et Littéraire in Brussels (end-of-year period 1904-1905) he exhibited various works under the heading "Souvenirs du Littoral". In 1906, together with Fernand Khnopff, Henry Stacquet and Henri Cassiers, he founded the "Société Internationale de la peinture à eau".

Charlet painted landscapes, marines, urban scenes, genre scenes and portraits. Initially he worked realistically, in line with the style of Bastien-Lepage. He soon appropriated a lighter color and a freer touch. Something that was obvious to him, given his many contacts in Paris (including with Paul Signac). George Seurat's theoretical pointillism charmed him only momentarily. Charlet rather remained focused on a free impressionism with loose, vibrating keys, with a lot of attention for light and reflections. Contemporary motifs were no stranger to him, such as ladies playing tennis or summer coastal life.