No longer active, former leader of Conservatives put in shade (7)
I believe the answer is:
extinct
'no longer active' is the definition.
(as in an extinct volcano)
'former leader of conservatives put in shade' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'leader of' says to take the initial letters.
'put in' indicates putting letters inside.
'shade' becomes 'tint' (synonyms).
The first letter of 'conservatives' is 'c'.
'c' going within 'tint' is 'tinct'.
'ex'+'tinct'='EXTINCT'
(Other definitions for extinct that I've seen before include "(Of a volcano) dead" , "never to be seen again" , "No longer in existence" , "No longer erupting" , "Long gone, like te dinosaur" .)