Reclusive by nature, a character trait that became more exaggerated in the 1940s and later, Kelly's work reflects his determination not to be limited by the trends of his time.

The prosperity of the firm enabled his father to purchase a 144-acre farm in Bucks County, Pennsylvania in 1902, which he named "Rural Retreat"[1] It was here that Pantaleon took Leon to spend every weekend away from the pressures of business and from the disappointments in his failing marriage.

Being too young to enlist, he joined the Quartermaster Corp at the Army Depot in Philadelphia, where he served for more than a year loading ships with supplies and, along with other artists, working on drawings for camouflage.

Broken by circumstance, Pantaleon left Philadelphia to begin a wandering existence looking for work leaving Kelly to support his mother and grandmother.

During the day he was granted permission to study anatomy at the Philadelphia School of Osteopathy where he dissected a cadaver and perfected his knowledge of the human figure.

In the next three years Kelly's work ranged from academic studies of plaster casts, to pointillism, to landscapes of Fairmount Park in Philadelphia, as well as a series of pastels showing influences from Matisse to Picasso.

Influenced by Earl Horter's collection and Arthur Carles, he mastered analytical cubism in works such as The Three Pears (1923) and in 1925 experimented with Purism in Moon Behind the Italian House.

Patrons during this time were the police official Leon Zamaran, a collector of Courbets, Lautrecs and others, who began collecting Kelly's work.

The Little Gallery of Contemporary Art purchased the Absinthe Drinker in 1931 and in 1932 exhibited Judgement of Paris (1932), an ambitious painting with a classical theme.

In October 1934, "Interior of a Slaughter House" and several other works were included in "Second Regional Exhibition of Painting and Prints by Philadelphia Artists" at the Whitney Museum in New York.

Kelly's study of the masters in the Louvre collection resulted in great admiration for the Renaissance painter Leonardo da Vinci.

A small artists colony existed during summers in the town but in the winter it was reclaimed by the year round population of clammers, dredgers and fishermen.

In the stillness of this place his observations of dragonflies, birds and insects in the garden began to translate into a delicacy of line and a language of shapes that would come to characterize his paintings and especially his drawings.

In 1940, Helen Horter had contacted Julien Levy, a Harvard classmate of her brother-in-law Paul Vanderbilt, to propose an exhibition of drawings by Kelly.

His stable included Salvador Dalí, Arshile Gorky, Yves Tanguy, Roberto Matta, Max Ernst, Joseph Cornell and Marcel Duchamp.

The concept for the show was formulated by Marcel Duchamp and Levy and they invited 32 artists (the number of chess pieces in a set) to participate.

[12] Kelly, who did not play chess, confined his participation to a painting of a double landscape, the dominant larger one depicting a receding plane marked out as a chessboard surrounded by dark spindly leafless trees and cliffs.

[13] Though Levy closed his gallery in 1949 and left New York to take up residence in Connecticut, he and Kelly continued a friendship and working relationship through the 1950s.

On a Christmas vacation from teaching he traveled to New Mexico to visit family friend Edith Warner and the San Ildefonso Indians.

The Lunar series was born out of the experience of the quiet nights when Kelly and his dog Rusty would walk down the street to the bay before bed.

Combined with the delicate line inspired by insects physiology, the lunar figures described an emotional response to the moon's pale nocturnal presence.

In subsequent years his work is distinguished by a quality of drawing that bore out Alfred Barr's opinion in 1944 that "Kelly was one of the best American draftsmen".

The environment of the island provided Kelly with abundant subject matter from still life to bathers who were transformed into abstract frolicking designs reminiscent of the Lunar figures.

A trip to North Africa during this time resulted in themes of veiled figures such as those seen in a large drawing "The Harem in Generalife", 1963, currently in a New York City collection.