Cornoyer illustrated for the St. Louis newspapers while he attended the St. Louis School of Fine Arts. In 1889 he went to Paris where he studied at the Acad‚mie Julian under Laurens, Constant and Lefebvre, and received private criticism from Deguau-Bouveret. Summers were spent in Venice.
In 1894 he returned to St. Louis where he continued to paint and established his reputation on painting rainy-day Parisian street scenes and Venetian scenes. William M. Chase took an interest in his work, purchased one of his works, and encouraged him to come to New York. Cornoyer came to New York in 1899 and the following year began teaching at the Mechanics Institute. In New York he painted street scenes of the city, including views of Madison Square, Columbus Circle and Central Park, often featuring the weather effects of snow or rain.
He spent summers in Woodstock, Cos Cob and Gloucester, finally settling in Gloucester in 1907.
Corneyer was a charter member and officer of the North Shore Arts Association in Gloucester. While there he began to do paintings featuring the tonal and atmospheric qualities of late afternoon and moonlight.
