Equal rights advocate, finest — I’m converted! (8)
I believe the answer is:
feminist
'equal rights advocate' is the definition.
(someone wanting equal rights for women)
'finest i'm converted' is the wordplay.
'converted' is an anagram indicator.
'finest'+'im'='finestim'
'finestim' with letters rearranged gives 'FEMINIST'.
(Other definitions for feminist that I've seen before include "I'm finest as activist in women's lib movement" , "Mine's fit (anag.)" , "Advocate of women's rights" , "I'm finest (anag.)" , "I'm finest with supporter of women's lib" .)