In Nohant, where he lived with George Sand from 1839, Chopin produced numerous masterpieces. On October 20, 1841, Chopin wrote from Nohant to his friend Fontana in Paris, stating, "Today the Fantaisie is finished." Around 1841, Chopin was in a very fulfilling period both health-wise and in his relationship with Sand. During this time, in addition to the Fantaisie, Op. 49, he composed works such as Tarantelle, Op. 43, Polonaise in F-sharp minor, Op. 44, Prelude, Op. 45, Allegro de Concert, Op. 46, Ballade No. 3, Op. 47, and two Nocturnes, Op. 48. Consequently, these pieces influenced each other, blurring the boundaries of instrumental genres classified as character pieces, while each gaining depth and freedom.

The term "fantaisie" (fantasia), used in instrumental works, has a long history. While "fantasia" as a piano solo piece was not uncommon in the 19th century, it is questionable whether Chopin held a clear genre consciousness for this term. Regarding the Polonaise, Op. 44, composed just before, Chopin initially wrote that it was "a Fantaisie in the form of a Polonaise" or "more of a Fantaisie than a type of Polonaise." Furthermore, the existence of his late masterpiece, the Polonaise-Fantaisie (Polonaise=Fantaisie), suggests that Chopin regarded the polonaise and the fantaisie as very closely related. He seems to have assigned the "fantaisie" form the role of freely expressing not only improvisational colors but also his thoughts and fantasies about his homeland, Poland.

Ultimately, Op. 49, Chopin's only Fantaisie, begins in F minor and ends in A-flat major. If the work is viewed in a sonata-form-like manner, it would consist of an Introduction (Tempo di marcia), Exposition (agitato; mm. 68–), Development (mm. 143–, with an intervening Lento sostenuto episode), Recapitulation (mm. 236–), and Coda (mm. 309–). However, fitting the title of "Fantaisie," it is more natural to interpret it as a free interplay of keys and musical ideas. The F minor introduction, marked "Tempo di marcia" (in march tempo), is shrouded in a dark shadow reminiscent of a funeral march, progressing heavily with chords on each beat. In contrast, the A-flat major coda (mm. 322–), marked "Assai allegro," culminates brilliantly with triplet arpeggios, ending as if a declaration of victory. These two keys and two musical ideas seem to dominate the work as Chopin's two fantastical sentiments towards Poland. Triplet runs, accompanied by improvisational changes, support the core themes that constitute the piece (mm. 68–, 155, 235), or function as transitional passages (mm. 43–, 143–, 223–). Furthermore, chordal musical ideas, while seemingly forming march-like transitional sections (mm. 127–), also passionately sing out lyrical melodies with the "Lento sostenuto" tempo marking (mm. 199–). The Fantaisie, which combines formality and improvisation, and freely expresses thoughts of Poland while maintaining an asymmetrical symmetry, creates Chopin's unique world and can be positioned as a central work among the masterpieces leading to the Polonaise-Fantaisie.