Independent MP Alex Greenwich is suing Mark Latham for aggravated damages, claiming the NSW One Nation leader defamed him in a graphic and homophobic tweet accusing him of engaging in "disgusting" sexual activities.
Mr Latham posted the tweet in March in response to Mr Greenwich calling him a "disgusting human being" after LGBTQI protesters were attacked outside a forum where he was speaking.
Mr Latham deleted the tweet not long after but refused to apologise.
He was then quoted in the Daily Telegraph on April 1, saying "when (Mr Greenwich) calls someone a disgusting human being for attending a meeting in a church hall, maybe attention will turn to some of his habits".
Mr Greenwich is an openly gay man and the former convenor of Australian Marriage Equality, which led the campaign for same-sex marriage.
The Sydney MP filed a statement of claim in the Federal Court, seeking aggravated damages against Mr Latham as well as an injunction to stop the him from republishing the comments.
Mr Greenwich claims he has been exposed to hatred, contempt and ridicule as a result of the comments, and his personal and professional reputation has been "gravely injured".
"(Mr Greenwich) has suffered and will continue to suffer hurt, distress and embarrassment," the statement of claim, released by the Federal Court on Thursday, read.
Mr Greenwich alleges Mr Latham's tweet conveyed defamatory meanings that he "engages in disgusting sexual activities" and is "not a fit and proper person to be a member of the NSW parliament because he engages in disgusting sexual activities".
The MP claims Mr Latham continued to make defamatory comments following the newspaper article, including via a series of tweets.
Mr Greenwich's lawyers sent a defamation concerns notice to Mr Latham on April 19 but the NSW One Nation leader's solicitor declined a settlement offer on May 17.
Mr Latham is expected to file a defence to the statement of claim on July 28.
The matter is listed for a case management hearing in the Federal Court in September.
