Bromwich was born Rachel Sheldon Amos in Hove, Sussex (some obituaries said Brighton),[2] in 1915, and spent her early childhood in Egypt.

[4] In 1934 Rachel Amos attended Newnham College, Cambridge, where she studied the Anglo-Saxon language before shifting departments to focus on Middle Welsh.

[4] In 1961 Bromwich published Trioedd Ynys Prydein, her influential edition of the Welsh Triads.

[6] This is considered "a central work of the scholarship on medieval Welsh literature", according to her Cambridge obituary.

[2] Her other major contribution to Welsh scholarship was her series of books and articles on Dafydd ap Gwilym, the outstanding Welsh poet of the period, mostly summarised in Aspects of the Poetry of Dafydd ap Gwilym (Cardiff, 1985).