[1] When Reni was about twenty years old, the three Calvaert pupils migrated to the rising rival studio, named Accademia degli Incamminati (Academy of the "newly embarked", or progressives), led by Ludovico Carracci.

[1] By late 1601 Reni and Albani had moved to Rome[2] to work with the teams led by Annibale Carracci in fresco decoration of the Farnese Palace.

[4] The building was originally a pavilion commissioned by Cardinal Scipione Borghese;[5] the rear portion overlooks the Piazza Montecavallo and Palazzo del Quirinale.

[6] The massive fresco is framed in quadri riportati and depicts Apollo in his Chariot preceded by Dawn (Aurora) bringing light to the world.

[7] The work is restrained in classicism, copying poses from Roman sarcophagi, and showing far more simplicity and restraint than Carracci's riotous Triumph of Bacchus and Ariadne[8] in the Farnese.

[citation needed] In 1630 the Barberini family of Pope Urban VIII commissioned from Reni a painting of the Archangel Michael for the church of Santa Maria della Concezione dei Cappuccini.

[9] The painting, completed in 1636, gave rise to an old legend that Reni had represented Satan—crushed under St Michael's foot—with the facial features of Cardinal Giovanni Battista Pamphilj in revenge for a slight.

He also contributed to the decoration of the Rosary Chapel in the same church with a Resurrection; and in 1611 he had already painted for San Domenico a superb Massacre of the Innocents (now in the Pinacoteca Nazionale di Bologna) which became an important reference for the French Neoclassic style, as well as a model for details in Picasso's Guernica.

The painting is thought to have been a commission for a member of the papal court due to the presence of lapis lazuli in the blue of the sky, an expensive material usually supplied by clients.

In contrast, his Crucifixion and his Atlanta and Hipomenes[15] depict dramatic diagonal movement coupled with the effects of light and shade that portray the more Baroque influence of Caravaggio.

According to his biographer, Carlo Cesare Malvasia, Reni's need to recoup gambling losses resulted in rushed execution and multiple copies of his works produced by his workshop.

He painted few portraits; those of Sixtus V and of Cardinal Bernardino Spada are among the most noteworthy, along with one of his mother (in the Pinacoteca Nazionale di Bologna) and a few self-portraits – both from his youth and from his old age.

[11] Reni's other Bolognese pupils included Antonio Randa (early on in his career considered the best pupil of Reni, until he tried to kill his master), Vincenzo Gotti,[18] Emilio Savonanzi,[19] Sebastiano Brunetti,[20] Tommaso Campana,[21] Domenico Maria Canuti,[22] Bartolomeo Marescotti,[23] Giovanni Maria Tamburino,[24] and Pietro Gallinari (Pierino del Signor Guido).

In the 19th century, Reni's reputation declined as a result of changing taste—epitomized by John Ruskin's censorious judgment that the artist's work was sentimental and false.