John Korn was initially hired by Mr Lehrmann after Brittany Higgins alleged he raped her inside Parliament House after a night out.
Mr Lehrmann has always denied the allegation.
The defence lawyer will be the eighth witness to front the inquiry established by the ACT government to examine how the justice system handled the high-profile case.
In his statement to the inquiry, Mr Korn said an "active media campaign" by Ms Higgins had "trashed the concept of a fair trial".
He also accused ACT Director of Public Prosecutions Shane Drumgold of not doing enough to safeguard the trial.
"A fair trial meant fair to Ms Higgins, fair to Mr Lehrmann and most of all fair to the Australian community," Mr Korn said.
"Allowing (Ms Higgins) to go on the podium as a survivor of a sexual assault with the trial coming up is something that the director had a responsibility to try and actively prevent."
Mr Korn raised concerns with the chief prosecutor about a joint address Ms Higgins was due to give at the National Press Club in Canberra with 2021 Australian of the Year Grace Tame.
He said Mr Drumgold told him Ms Higgins had been "appropriately warned" not to give any details about the alleged offence during her speech.
Ms Higgins' address ultimately went ahead in February 2022 and attracted widespread media coverage.
Mr Lehrmann has since launched defamation proceedings against the ABC for its live broadcast of the address, which the public broadcaster is fighting.
"Even if (Mr Drumgold) was unsuccessful, as the first law officer of the ACT ... he had a prime obligation to try and do what he could to ensure a fair trial for all," Mr Korn said.
ACT Victims of Crime Commissioner Heidi Yates is also expected to front the inquiry.
Ms Yates provided support to Ms Higgins throughout the investigation and accompanied her to the trial each day.
Police officers accused Ms Yates of "interfering" in their investigation but later reversed these criticisms when the inquiry presented evidence of her assistance.
Mr Lehrmann faced an ACT Supreme Court trial in October 2022 that was derailed due to juror misconduct.
He was represented at trial by defence lawyer Stephen Whybrow.
Prosecutors later dropped the charge against him due to fears about the impact a second trial would have on Ms Higgins' mental health.
6°C