In 1625, after a brief visit to Venice, he arrived in Rome where artistic life was dominated by Bernini. For many years Algardi earned his living by restoring antiques and making small models which were cast either in bronze or in precious metals. His first major commission was for the tomb of Pope Leo XI in St Peter's (1634 - 44), followed by that for the marble St Philip Neri in the sacristry of the Vallicella (1635? - 46). Some of his rivals in Rome doubted his ability to work in marble. To silence them he carved Sleep (1635 - 6) in the harder medium of black marble (Museo e Galleria Borghese, Rome). Meanwhile, for the high altar of the Spada church of S. Paolo in Bologna, he produced the two-figure marble group of the Beheading of St Paul.

With the election of Innocent X in 1644 and the disgrace of Bernini, Algardi had a chance to exercise his talents more extensively. He carved the high-relief altarpiece of Leo and Attila in St Peter's (1646 - 53), the altar group of St Nicholas of Tolentino (begun 1651; S. Nicola da Tolentino, Rome); and made the full-scale model for the unexecuted altar relief of the Miracle of St Agnes (Vallicella, Rome). He also designed the delicate stucco reliefs of the Villa Pamphili which were to prove so influential for the Neoclassicists of Robert Adam's generation.

Throughout his life, Algardi produced numerous portrait busts, many of them for tombs. They are marked by a feeling for solidity and a sensitivity to surface texture and detail, and are imbued with a straight-forward naturalism and life-like veracity.

As the principal rival to Bernini, Algardi is often regarded as a classicist, and indeed his major sculptures in white marble are comparatively detached and undramatic, avoiding the more spectacular effects of the Baroque. But he displays an inventive talent in his decorative ornamentation.