Ruth Tomalin grew up in West Sussex on the Stansted Park estate, where her father was head gardener. She was educated at Chichester High School, Sussex, and then at King's College London, where she received her diploma of journalism in 1939. She served from 1941 to 1942 at Bosham in the Women's Land Army. From 1942 to 1961 she was a reporter for newspapers in Hampshire, Sussex, Dorset, and Hertfordshire. From 1961 she was a part-time court reporter in London.
Ruth Tomalin's work falls into two distinct categories. There are several short novels for children of 9 to 10, the best of which is A Stranger Thing. There is also a group of novels concerned with the childhood and youth of Ralph Oliver and latterly his young cousin Rowan — The Garden House, The Spring House, and Away to the West: these are longer and far more exacting works, so difficult to classify that in the judgement of some critics they are adult novels and cannot be regarded as children's books at all.
In 1942, she married Vernon Leaver. They had one son but the marriage ended in divorce. In 1971, she married William N. Ross, who predeceased her.
- The Day of the Rose: Essays and Portraits. 1947.
- Threnody for Dormice. 1947. (verse)
- as Ruth Leaver: Green Ink. 1951. (for children)
- All Souls. 1952. (novel)
- Deer's Cry. 1952. (verse)
- W. H. Hudson: An Autobiography. 1954.
- as Ruth Leaver: The Sound of Pets. 1955. (for children)
- The Daffodil Bird, illustrated by Brian Wildsmith. 1959. (for children)
- The Sea Mice, illustrated by Sheila Rose. (for children)
- The Garden House. 1964. (novel)
- The Spring House. 1968. (novel)
- Best Country Stories; edited, with an introduction, by Ruth Tomalin. 1969.
- Away to the West. 1972. (novel)
- A Green Wishbone, illustrated by Gavin Rowe. 1975. (for children)
- A Stranger Thing, illustrated by Robin Jacques. 1975. (for children)
- The Snake Crook. illustrated by Shirley Hughes. 1976. (for children)
- Gone Away. 1977. (Francie book series, 1 of 2)
- Little Nasty, illustrated by Sue Scullard. 1985.
- A Summer Ghost. 1986.
- Another Day. 1988. (Francie book series, 2 of 2)
- Long Since. 1989.
- "Tomalin, Ruth (1919–2012), fonds". King's College London.
- Kirkpatrick, D. L., ed. (1978). ""Tomalin, Ruth" by Peter Hollindale". Twentieth-century Children's Writers. pp. 1234–1235.
- Burton, John A. (1983). "Review of W. H. Hudson: a biography by Ruth Tomalin" (PDF). Oryx. 17 (3): 147–148. doi:10.1017/s0030605300029562.
- "Review of Gone Away by Ruth Tomalin". Kirkus Reviews. 1 June 1979.