Originally trained under Antonio Balestra, Longhi began his career as a painter of altarpieces and history paintings; by the second half of the 1730s, however, he had begun to paint the small-scale genre works for which he is renowned. In 1741 he signed and dated The Concert (Venice, Accademia), an interior view of Venetian noble life, his first surviving signed and dated work after the frescoes of The Fall of the Giants of 1734 (Ca' Sagredo, Venice). Sources suggested for Longhi's genre pictures include Crespi and also William Hogarth and Antoine Watteau, whilst such fashionable interior scenes as The Concert or The Introduction (Paris, Louvre) appear to derive, at least in part, from seventeenth-century Dutch genre pictures, which were far from rare in eighteenth-century Venice.
Longhi's pictures are painted in colours that are clear and clean, and they show a deep appreciation of the texture of fabrics, which are occasionally enlivened with flickering splashes of colour. His numerous surviving drawings (over 150 in Venice, Correr) are excellent examples of draughtsmanship, effortlessly capturing the gesture and features of his subjects, some of which were observed from life. His abilities were such that he was instructor to the life class at the Accademia dei Pittori until 1780 and the founder-director of the academy of drawing and engraving at the Palazzo Pisani. Longhi was immensely popular in his day, lionized as an outstanding imitator of nature and compared favourably to Tiepolo.