Career complete, ultimately knackered, went to bed (7)
I believe the answer is:
retired
'went to bed' is the definition.
('retire' can be a synonym of 'go to bed')
'career complete ultimately knackered' is the wordplay.
'ultimately' suggests the final letters.
'knackered' becomes 'tired' (I've seen this before).
The last letters of 'career complete' are 're'.
're'+'tired'='RETIRED'
(Other definitions for retired that I've seen before include "No longer working" , "Gone to bed" , "out of office?" , "Stopped working" , "Pensioned off" .)