Ernest Rouart was a French painter, watercolorist, pastellist, engraver, and art collector.

He was one of four sons and a daughter born to the engineer and painter, Henri Rouart. His brother, Eugène [fr], was a well known politician. He began by studying mathematics; intending to enter his father's business but, like his father, he turned to painting, enlisting the aid of Edgar Degas, a family friend, who gave him lessons and advised him to copy paintings at the Louvre. He also had him experiment with older mixtures of paint, as they were prepared in the Renaissance.

It was also Degas who introduced him to the model and future art collector, Julie Manet, daughter of the painters Berthe Morisot and Eugène Manet They married soon after, in 1900, and would have three sons.

He was an avid art collector, as was his father. In 1912, he and his siblings decided to sell their late father's collection; which went for a considerable sum. Shortly after the beginning of World War I, in 1914, he obtained permission to hold a sale of Degas' paintings. His friend, then eighty years old, had fallen on hard times and needed assistance.

After beginning his career as a painter, he held numerous exhibits; first at the Société Nationale des Beaux-Arts in 1899. Later, he had showings at the Salon des indépendants [fr], and the Salon des Tuileries. He was a member of the governing committee for the Salon d'Automne. In 1932, he organized the "Exposition du Centenaire de Manet" at the Musée de l'Orangerie. Similar exhibitions followed, for Degas in 1934, and Berthe Morisot in 1941.

He died during the German occupation of Paris, and was interred at the Cimetière de Passy.