A person who believes in or supports secularism(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "secularist" in a sentence
"The leader of Turkey 's main secularist opposition is tearing up the rule book of the party that Ataturk built, as he tries to build a credible alternative to the government of Prime Minister Recep Tayyip Erdogan."
"Turkey has been a hotbed of debate between Islam and secularism recently with the election of President Abdullah Gül, whose first bid was blocked by the Constitutional court in secularist concern for his views on Islam and the fact his wife wears the hijab."
"Seems to me the the motto of the secularist is "the only good Christian is a silent one.""