It emerged on Thursday evening that members of the Scottish Government Handling of Harassment Complaints Committee voted 5-4 that Ms Sturgeon gave an “inaccurate” account of a meeting with her predecessor Alex Salmond during the live investigation.
Mr Wightman, who sits on the nine-strong committee as an independent, is thought to have the deciding vote between the four SNP colleagues and the four representing the Scottish Conservatives, Labour and Lib Dems.
The Lothians region MSP took to Twitter on Friday morning to post an excerpt from section seven of the MSP code of conduct that states leaks to the press can “seriously undermine and devalue the work of committees”.
The passage read: “Unless the Parliament or the relevant committee has agreed otherwise, such documents must not be circulated, shown or transmitted in any other way to members of the public (including those in Cross-Party groups), media or to any member of any organisation outwith the Parliament, including the Scottish Government, nor to other MSPs who are not members of the committee or committees for whom the material was intended.
“Members must not provide the media with any other briefings or views on the general contents or ‘line’ of draft committee reports or other confidential material or information.”
The passage concludes: “Disclosures of this kind can also seriously undermine and devalue the work of committees.”
Mr Wightman’s intervention comes after the First Minister told reporters outside her Glasgow home she was not surprised by the “very partisan” leak.
She told Sky News: “I stand by all of the evidence I gave to the committee, all eight hours’ worth of evidence.
“What’s been clear is that opposition members of this committee made their minds up about me before I muttered a single word of evidence. Their public comments have made that clear.
“So this leak from the committee – very partisan leak – tonight before they’ve finalised the report is not that surprising.”
Ms Sturgeon said she was awaiting the result of the James Hamilton QC investigation into whether she broke the ministerial code.