He is best known for his female nudes, painted in a fashion similar to that of his friends Frederick Carl Frieseke, Lawton S. Parker, and Richard E. Miller, all American artists who studied and lived in France.
Ritman was a member of the second generation of American artists to work in Giverny, where he first painted in 1911 and would continue to summer for the next twenty years.
He and his contemporaries preferred the female nude as their subject, painted in dappled sunlight or in chromatic interiors.
While his work bears strong similarities to Frieseke's, art historian William H. Gerdts notes "an appealing wistfulness which is also quite distinct.
In 1929 Ritman returned to the United States to instruct at the School of the Art Institute of Chicago, yet continued to visit France until the end of his life.