Love book about marvellous biographer (7)
I believe the answer is:
boswell
'biographer' is the definition.
(I've seen this before)
'love book about marvellous' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'book' becomes 'b' (abbreviation for book).
'about' is a reversal indicator.
'marvellous' becomes 'swell' (I've seen this before).
'o'+'b'='ob'
'ob' written backwards gives 'bo'.
'bo'+'swell'='BOSWELL'
(Other definitions for boswell that I've seen before include "James --, biographer" , "Companion and biographer of Samuel Johnson" , "diarist" , "Writer of Johnson's life" , "Bellows like Dr Johnson's biographer" .)