The 32-year-old is taking leave from the party room after seven Greens members wrote a letter demanding an investigation into his alleged conduct.
The alleged incidents spanned almost a decade, from when he was elected in 2017 to 2025.
The investigation will be handled by the Western Australian Greens branch, as a federal parliamentary body confirmed it would be unable to handle the concerns.
Legal advice on how that investigation should be conducted - including whether it will be made public and whether witnesses who were not signatories to the letter will be called - is now being sought.
"Everyone involved is entitled to natural justice and procedural fairness," the state branch's co-conveners Simone Collins and Giz Watson said.
"A process that is impartial from the outset is the best way to reach an outcome that all parties can have confidence in.
"We know that raising concerns can be difficult and we respect the courage it takes for anyone to come forward."
WA Greens did not answer other questions from AAP, saying it would be inappropriate to comment further.
Greens leader David Shoebridge confirmed Senator Steele-John would not be appearing in parliament while internal investigations took place.
"I'm glad that Senator Steele-John has agreed to refer the matter for a full, a fair and an independent and timely investigation," he told ABC TV on Friday.
"I can say that none of the signatories of the letter asserted to any direct knowledge of the matters involved and, of course, that creates some additional complexity in dealing with it."
He said it would not be up to him to decide if the investigation was made public, because the process would be commissioned by the WA Greens.
He had a discussion with the senator before the letter was made public, in which leave was agreed to.
Senator Steele-John has "utterly rejected" the claims in a statement to media and alleges he was the victim of assault in a previous relationship.
Senator Shoebridge has denied previous knowledge of the allegations.
A source inside the youth wing of the party's NSW branch told AAP Senator Steele-John had been raised in connection with allegations of sexual harassment as early as October 2018.
At the time, a general meeting of the state's Young Greens directed their national delegates to block and indefinitely delay motions to formally investigate the WA senator for alleged sexual harassment.
In the same meeting, they also asked the delegates to keep voting to block Senator Steele-John from appearing on the party's social media pages.
Both motions were agreed to by consensus, the source said, and are the only times the WA senator's name appears in NSW Young Greens meeting minutes since before he entered the federal upper house.
Senator Shoebridge, who was a member of the NSW Legislative Council at the time, has said he does not remember any NSW Young Greens motion relating to Senator Steele-John.
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