She was born in England in 1947 to Irish parents; her mother was the composer Elizabeth Maconchy. LeFanu studied at Oxford, RCM and Harvard. She is active in many aspects of the musical profession and was Professor of Music at University of York, 1994-2008.

In April 2017 she celebrated her seventieth birthday, and was BBC Radio 3 ’Composer of the Week’. 2017 also saw premieres of five new works, including ‘The Crimson Bird’ a dramatic scena, text John Fuller; commissioned by RPS for BBCSO with Rachel Nicholls, soprano. The cantata ‘St Hilda of Whitby’, text Wendy Cope, was premiered in February 2018.

In 2020 a CD with four of her major orchestral pieces was released by NMC, supported by a grant from the PRSF. It features the RTE NSO and the BBCSO.

Premieres since the pandemic include LeFanu’s new work for saxophone orchestra ‘In The Forests of the Night’, premiered in New York and toured in Germany and UK; the Quintet for strings; ‘After Lindisfarne’ for solo horn; ‘Triptych’ for baritone and chamber orchestra (text, Rowan Williams), ‘Broadwood Bagatelles’ for clavichord and ‘the forest, the strand, the sea’ for solo piano.