Minartz was a self-taught painter. He created a significant body of work, particularly of skilfully rendered sketches and watercolours, which may be divided into two main series: Parisian life and society, and landscapes of the Côte-d’Azur.
On the Côte-d’Azur, his sketches trace an itinerary between St-Tropez and Cannes, by way of Nice and Monaco, and extending even to Venice. He depicted ports crowded with yachts and other boats, the beaches and their pleasant bustle. He was most known for his interpretations of Parisian life, of the Belle Époque through to the excesses of the 1930s.
He illustrated the vicissitudes of society life, and was a faithful chronicler of its parties, the casino, cabaret, circus shows and their backstage goings-on, the music-hall, the Opéra and its ballets. He showed in collective exhibitions from 1896 to 1914, most notably at the Salon de la Société Nationale des Beaux-Arts, of which he became an associate member in 1901.