August Friedrich Siegert was a German painter of the Düsseldorf School.

From 1835 August Siegert, the eldest son of a soap and candle manufacturer from Neuwied, attended the Düsseldorf Art Academy. In 1837 he was trained there by Theodor Hildebrandt, and from 1841 by Wilhelm von Schadow. From 1846 to 1848 he traveled through the Netherlands and Belgium, where he became acquainted with Belgian colorism in Antwerp, France and Italy. After a long stay in Munich, he lived in Neuwied for a few years and mainly painted portraits. In 1851 he settled in Düsseldorf. Until 1859 he headed a master's studio at the Düsseldorf Art Academy and taught there. In 1872 he was appointed professor.

Siegert was a member of the Düsseldorf artists' association Malkasten from 1850 to 1883 .

In 1852 Siegert married Mathilde de Haen, the only daughter of the paint, pharmacy and chemicals dealer Wilhelm de Haen and his wife Elisabeth Jacobine Carstanjen. The couple had two daughters and two sons. One of the sons, August Siegert (1858–1931), later headed the company de Haen-Carstanjen & Söhne GmbH, Düsseldorf.