Darwin was born and brought up in London. Her father is Henry Galton Darwin, a lawyer in the Foreign Office, son of Sir Charles Galton Darwin, grandson of Sir George Darwin, and great-grandson of Charles Darwin. Her mother Jane (née Christie) is an English teacher, so they spent three years commuting between London and Brussels. She has two sisters; Carola and Sophia (Sophia Katherine). The family spent many holidays on the Essex/Suffolk border, where much of her novel The Mathematics of Love is set.

She read Drama at the University of Birmingham, and she spent some years in academic publishing. But when she had two small children she started writing again, and eventually earned an MPhil in Writing at the University of Glamorgan, where her tutor was novelist and poet Christopher Meredith. The novel she wrote for the degree became The Mathematics of Love, which was sold to Headline Review, as the first of a two-book deal. Meanwhile, she had found the form of a research degree so fruitful that she is doing a PhD in Creative Writing at Goldsmiths' College, where her supervisor is Maura Dooley. Darwin now lives with her children in South East London, still surrounded by history: there was a Viking fort on the hill behind their house, and down the road is Eltham Palace.

The Mathematics of Love was shortlisted for the Commonwealth Writers Best First Book Award for the Europe and South Asia region.