The archive mainly comprises correspondence relating to Charles' activities as a Civil Servant and administrator. There are also publications relating to these activities and Charles' wider interests.

There is also personal content, including travel diaries, family correspondence and papers regarding inheritance of the Wallington estate in Northumberland.

This archive includes content accumulated and created by both Charles and Mary, and other family members. It reflects the family's personal activities from Charles' childhood in the 1870s to Mary's death in 1966, but also includes some content from Charles' professional life. It can support research into a broad variety of areas, including political history (particularly the Liberal and Labour parties, socialism and international relations), World War I (particularly dissent and the peace movement), childhood and education (from both a personal and political perspective), domesticity, class and landed estates.
This extensive personal archive is mostly comprised of correspondence. This includes: Correspondence to Charles in his role as MP Correspondence to and from Charles relating to the operation of the Union of Democratic Control Correspondence to and from Charles relating to his positions in government Correspondence relating to the management of the Wallington estate and the donation to the National Trust Correspondence between members of the Trevelyan and Bell families, much of which is domestic in tone Correspondence to and from Charles and Mary's children from their early childhood to adulthood Correspondence from visits abroad including North America, Australia, New Zealand, the Middle East, Russia and Germany The correspondents include family members such as Charles' brothers George Macaulay Trevelyan and Robert Calverley Trevelyan, Mary's sister and brother in law Elsa Richmond and Admiral Sir Herbert William Richmond. Other correspondents include Sir Winston Churchill, J Ramsay MacDonald, E D Morel, Arthur Ponsonby, Walter Runciman, Herbert Samuel, George Bernard Shaw and Jennie Lee.

Other documents include: Papers relating to Charles, Mary and their childrens' educations, including exam papers and school ephemera Personal Diaries, in particular a short run of Mary's personal diaries as a young woman Official political papers, including Cabinet Conclusions, draft bills[?] and copies of Hansard Pamphlets and leaflets written by and collected by Charles, many relating to socialism and the UDC Transcripts of speeches given by Charles and Mary in professional and personal capacities Personal notebooks with draft speeches and essays Family photograph albums and glass negatives, recording family events, daily life, and Charles' political career Press cuttings and scrapbooks relating to family events and Charles' career

The Wallis Collection contains books on mathematics and maths education and includes works by Robert Record (the man who introduced the = symbol), such as The grounde of artes: teaching the perfecte worke and practise of arithmetike (1582) and works by and about Isaac Newton, such as Newton's Principia in its first American edition (1846).

The books were formerly owned by Peter Wallis (1918-1992), a lecturer in the School of Education. There are almanacs, works on algebra and geometry, school text books, works on astronomy including J.F.W. Herschel's Astronomy (1835), guides to measuring, book-keeping, ready reckoners, treatises, Euclid's Elements and manuals.