Nini Lopez first appeared in the work of Auguste Renoir (1841–1919) in La Loge (The Theatre Box), painted in 1874. The young woman from Montmartre, cruelly nicknamed Nini-Gueule-de-Raie, or "fish face", is shown alongside the artist's brother. Although the artwork was immediately purchased by the art dealer "le Père Martin", Renoir, like many of his Impressionist friends, was experiencing serious financial difficulty at the time. In the spring of 1875, he moved into a new studio on rue Cortot in Montmartre. The painter liked the almost wild quality of the garden, where Nini posed for him regularly. Known for being serious and punctual, the young woman become the artist's favourite model between 1875 and 1879, appearing in at least fourteen paintings.

The Portrait of Nini Lopez was painted in 1876, the year the artist outshone himself in breathtaking compositions such as The Swing or Dance at Le Moulin de la Galette. But at the time, Renoir was also painting numerous intimate scenes and smaller portraits for commercial purposes. The canvas purchased by collector Olivier Senn from Le Havre is very similar to a smaller work, Portrait of Nini Lopez (Blond Profile), in which the young woman is dressed in the same clothes: black and white bodice, green scarf and black ribbon tying back her hair. The model has the same soft features that give Nini her dreamy charm.

The painting, which places great emphasis on the study of light behind the model, was undoubtedly executed near one of the windows that opened onto the garden of the studio on rue Cortot. Renoir was striving to convey the changing reflections of light on the human figure.

A study conducted by C2RMF, the centre for the research and restoration of French museums, revealed that Renoir had taken a canvas already painted—a horizontal landscape—and turned it vertically before enlarging it with two bands. The artwork shows traces of this story—thick brushstrokes underlying the woman's face, an almost sketch-like treatment of the side edges—, and the ensuing freedom of execution lends an extraordinary modern quality to the work as a whole.

In 1877, as Renoir's talent as a portrait artist earned him prestigious commissions with the bourgeoisie, Nini disappeared from his painting following her marriage to a third-rate actor in the Montmartre theatre, much to the dismay of her mother and the artist, who had become her protector, for they had both dreamed of a bourgeois marriage for her. But during the six years she posed for the artist, the young Nini incarnated Renoir's feminine ideal, filled with happiness and joy of life.