Delattre was a faithful friend Charles Angrand and Claude Monet, the fierce advocates of new ideas and Impressionism.

His first paintings form part of the Barbizon school tradition, progressively evolving with greater freedom, simplified shapes, and faded contours lines.

[1] In 1895 Delattre founded the Académie libre (Free Academy) on rue des Charrettes in Rouen.

The workshop, including excursions outdoors to work En plein air at Pré-aux-Loups or Côte Sainte-Catherine, became a rallying point for young independent artists of the new generation of l'École de Rouen.

Admired by a generation of artists from Rouen, he wrote modestly: "Je n'aurai donné qu'un petit son de flûte mais il aura été juste".