A notable researcher of Viking activity in the British Isles, Mawer is best known as the founder of the English Place-Name Society, and as Provost of University College London from 1929 to 1942.

He was born the second child and eldest son of five children, to George Henry Mawer of South Hackney and Clara Isabella Allen.

[2][3] Mawer entered Coopers' Company Grammar School at the age of ten, where he won a scholarship at the end of his first term.

[4] Mawer entered Gonville and Caius College, Cambridge, in October 1901 as a foundation scholar, residing there for three years, obtaining a double mark of distinction in the English sections of the Medieval and Modern Languages Tripos.

Supported by a Research Studentship given to him by the college, he spent the next year studying Viking activity in England, in particular the subject of Old Norse place-names.

[7][8] In the preface to this work, Mawer laid down his principle that "no single county can be dealt with satisfactorily apart from a survey of the field of English place-nomenclature as a whole".

[6] In 1921, Mawer became Baines Professor of the English Language at the University of Liverpool, succeeding Henry Cecil Kennedy Wyld.

Drawing upon large support from the English public, the Society gained many members and plenty of funds, and its Survey came to be conducted by several scholars, including Eilert Ekwall, Frank Stenton, Percy Hide Reany, Albert Hugh Smith, John Eric Bruce Gover and Mawer himself.

In the latter article, which has been described as his most important work on history, Mawer convincingly argued that the ethnic distinction between Danes and Norwegians was a significant political factor in tenth-century England.

[14] His strenuous efforts to hold the college together during wartime took a heavy toll on Mawer's health, and on 22 July 1942 he collapsed and died suddenly on a train in Broxbourne while on his way to a meeting of a committee in London.