The Collaborative International Dictionary of English v.0.48:

Abiogenist \Ab`i*og"e*nist\, n. (Biol.)
   One who believes that life can be produced independently of
   antecedent. --Huxley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abiogenist
    n 1: a believer in abiogenesis