A writer’s saga: thrice a hit novel (6,8)
I believe the answer is:
agatha christie
'a writer's' is the definition.
(I've seen this before)
'saga thrice a hit novel' is the wordplay.
'novel' indicates an anagram (letters in a new or novel order).
'saga'+'thrice'+'a'+'hit'='sagathriceahit'
'sagathriceahit' anagrammed gives 'AGATHA CHRISTIE'.
(Other definitions for agatha christie that I've seen before include "Detective story writer" , "[THE QUEEN OF CRIME] - with 16d" , "author" , "One who wrote" .)