Police confirmed in a statement on Thursday they received a report of a man assaulting a woman in December last year.
The people involved were employed at parliament house at the time but are not politicians or political staff.
An ACT policing spokesman said the incident involved “building support staff” and was reported in March.
“Specialist investigators from the Sexual Assault and Child Abuse Team have spoken to the complainant and they have advised they do not wish to proceed with an investigation,” he told AAP.
“Support services have been offered to the complainant and if (she) wishes to proceed – the matter can be re-opened at any time.”
A Department of Parliamentary Services spokeswoman said an investigation into the incident was underway.
“Allegations of sexual assault reported to (the department) are referred to police as a matter of course,” she said.
The incident occurred within a year of News Corp revealing Brittany Higgins, a former Liberal staffer, was allegedly raped in Linda Reynolds’ ministerial office in March 2019.