In a writ lodged with the Supreme Court of Western Australia, the local senator claimed Mr Sharaz falsely defamed her via two tweets posted in 2022.
Ms Higgins alleged she was raped in 2019 by Bruce Lehrmann inside Senator Reynolds' ministerial office, for whom they both worked as staffers.
Mr Lehrmann consistently denied the allegation, and his trial in the ACT Supreme Court was derailed by juror misconduct.
Prosecutors decided not to pursue further action.
Senator Reynolds on Friday confirmed she engaged "leading defamation lawyers", and pointed to Mr Sharaz as a "constant participant" in trolling over Ms Higgins' case.
"For the best part of the last two years I have been the subject of harassing and highly distressing trolling on social media regarding myself and my conduct in respect of events concerning Ms Brittany Higgins which has damaged my reputation and caused me, my family and my staff, considerable stress and anguish," Senator Reynolds said in a statement to AAP.
"Mr Sharaz has been a constant participant in the trolling.
"In light of the conclusion of the criminal trial and the resolution of the civil action involving Ms Higgins and the Commonwealth, I am now at liberty to take steps to vindicate my reputation and provide some truth to the matters the subject of these trolling comments."
Senator Reynolds was seeking damages including aggravated damages, an injunction stopping Mr Sharaz from publishing the defamatory material or words similar, and interest on damages, according to the writ.
Law firm Arnold Bloch Leibler confirmed it was advising Mr Sharaz, but said it would not comment any further on the matter.
Perth firm Bennett confirmed it was representing Senator Reynolds.
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