The 32-year-old Western Australian senator has taken leave from the party room after seven members demanded an investigation into the alleged conduct.
Senator Steele-John is accused of concerning behaviour in the presence of women, with claims spanning almost a decade, from 2017 to 2025.
A letter sent to Greens leader David Shoebridge contained accusations he said the party would take "extremely seriously".
"As leader, I want to make it clear that the integrity of the complaints process is essential," Senator Shoebridge said.
"In the circumstances, Senator Steele-John has requested leave from the party room, and I have accepted it."
The senator will self-refer matters outlined in the letter to an independent complaints process.
In a statement, Senator Steele-John said the allegations were made without specifics.
"I utterly reject this characterisation of me, which tries to assert I am someone I am not," he said.
"Any allegation of this nature is extremely serious and must be treated accordingly. If someone has made an allegation, I am prepared to address it.
"I have referred this matter to the WA Greens, so that a fair, independent process can be commissioned that upholds the principles of natural justice and ensures procedural fairness for everyone involved."
The Greens leader said he was only told about the allegations against the senator in recent days and accepted the leave of absence from Senator Steele-John earlier in the week once he was made aware.
"I've dealt with it with the urgency which I think is appropriate," Senator Shoebridge told reporters in Canberra.
"I will not be engaging in a running commentary on the matter, because it is going to a fair and independent and timely process ... Senator Steele-John is entitled to that process."
Senator Steele-John entered parliament in 2017 when he was 23 and is the party's spokesman for disability and mental health, leading a campaign against NDIS cuts.
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