MSPs will order the public standards watchdog to investigate shamed former Holyrood minister Mark McDonald.
The SNP's James Dornan lodged a formal complaint with the Scottish Parliament's Standards Committee over the MSP's return to parliament this week.
Committee convener Clare Haughey said the committee had agreed "to issue a direction to the Ethical Standards Commissioner to conduct an investigation into this complaint".
Mr McDonald quit his ministerial role and the SNP after admitting inappropriate behaviour towards women.
In his written complaint to the committee, Mr Dornan said the presence of his ex-party colleague would be a "clear negation" of the duty of care the Scottish Parliament has to its staff.
Mr Dornan claimed in the letter he escorted a parliamentary staff member to a car outside Holyrood as she was "sure Mr McDonald was waiting for her".
He added: "As we left the building he was standing close to the exit, and I have no doubt he was indeed waiting for her."
He said the woman later became "so unwell with stress" she had a stroke, a situation he claimed was "compounded" by Mr McDonald, who denies both allegations.
The committee spent more than a hour considering the complaint in private before Ms Haughey made a public statement announcing the decision to have the Commissioner for Ethical Standards in Public Life investigate.
She said: "The Committee is currently conducting an inquiry into whether the MSP Code of Conduct is fit for purpose when dealing with complaints about sexual harassment and inappropriate conduct.
"There is still some way to go with our inquiry, but there appears to be an early consensus that a more robust process is required.
"There needs to be recognition of the sensitivities required when handling such cases and for there to be fairness to everyone concerned.
"And any new process will also have to try to reconcile openness and transparency, with privacy and a duty of care towards potentially vulnerable people."
She also highlighted Holyrood's code of conduct bans MSPs from disclosing complaints to the press at an early stage, following reports regarding Mr Dornan's letter.
Mr McDonald, who is sitting as an independent MSP for Aberdeen Donside, asked to be given a second chance on his return to Holyrood on Tuesday and he did not intend to "antagonise or upset" anyone by coming back.
An internal SNP investigation into allegations from three women identified "persistent" behaviour including inappropriate and unwanted text messages, unwanted attention and exploiting his position of power.
The married father-of-two had already resigned as childcare minister when the allegations first emerged in November.
He has faced calls to resign his seat from First Minister and SNP leader Nicola Sturgeon, as well as several MSPs and MPs, after he quit his party and issued a public apology last week.