Sir Oswald Hornby Joseph Birley MC RA ROI (31 March 1880 – 6 May 1952) was an English portrait painter and royal portraitist in the early part of the 20th century.

[6] Other subjects were many war-time leaders such as Generals Eisenhower and Montgomery, as well as Admiral Mountbatten and Air Marshal Trenchard.

A major retrospective exhibition of Birley's work was held at the Philip Mould & Company gallery on Pall Mall in 2007.

[13] The couple had two children: Birley died at his home in London on 6 May 1952, a week after returning from six-week trip to the United States where he received medical assistance.

Other descendants include the fashion designer and muse Loulou de la Falaise (1948–2011), who was married to Desmond FitzGerald, 29th Knight of Glin (1937–2011), and later to Thadée Klossowski de Rola, a French writer who is the younger son of the painter Balthus (1908–2001).