Three of his father's brothers, William, James, and Edwin, were politically active in various roles, including as Lord Mayor of London and as members of parliament.

[5] Early in the First World War Pethick-Lawrence joined with others in founding the Union of Democratic Control (UDC), a leading anti-war organisation of which he became Treasurer.

[10] Elizabeth Kempster was employed as their housekeeper in 1945 following an interview at Lincoln's Inn, and worked at their home, Fourways, in Surrey, where Sylvia Pankhurst was a frequent visitor.

Gladys Groom-Smith, interviewed in June and August 1976, was secretary to the Pethick-Lawrence's, working alongside Esther Knowles who trained her.

His older sister Annie Jane Lawrence (1863-1953) was responsible for building the open-air Arts and Crafts school The Cloisters in Letchworth Garden City.

His name and picture (and those of 58 other women's suffrage supporters) are on the plinth of the statue of Millicent Fawcett in Parliament Square, London, unveiled in 2018.