Worked until I had got ahead (6)
I believe the answer is:
toiled
'worked' is the definition.
(toiling is a kind of working)
'until i had got ahead' is the wordplay.
'until' becomes 'to' (I've seen this in other clues).
'had' says to put letters next to each other.
'got ahead' becomes 'led' (to lead is to be ahead).
'to'+'i'+'led'='TOILED'
(Other definitions for toiled that I've seen before include "Worked incessantly" , "Worked laboriously and long" , "Worked long and hard" , "Laboued long and hard" , "Struggled long and hard" .)