The most common and most likely answer to this crossword clue is the 3 plus 5 plus 2 plus 4 letter word THE FACTS OF LIFE
I've seen this crossword clue in The Times
T
H
E
F
A
C
T
S
O
F
L
I
F
E
Buddy explains!
The straight part
We know that "Biographer's material/what's known of it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case biographer's material/what's known of it = the facts of life.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.