One put on trial, eg, hoped thus finally to reform (8)
I believe the answer is:
sheepdog
'one put on trial' is the definition.
(as in sheepdog trials)
'eg hoped thus finally to reform' is the wordplay.
'finally' says to take the final letters.
'to reform' indicates an anagram.
The last letter of 'thus' is 's'.
'eg'+'hoped'+'s'='eghopeds'
'eghopeds' with letters rearranged gives 'SHEEPDOG'.
(Other definitions for sheepdog that I've seen before include "eg Border collie" , "Pastoral assistant?" , "Collie, perhaps" , "One drives over fields" , "Working farm animal" .)