OTTAWA -- Saskatchewan MP Erin Weir says he wants an external appeal of the harassment investigation about him earlier this year, arguing he was not afforded due process.

Weir is requesting an outside authority such as the House of Commons human resources office or a human rights tribunal to review the investigation process launched by NDP Leader Jagmeet Singh in the spring.

The three-month investigation, conducted by a University of Ottawa professor, found credible evidence to support one allegation of harassment and three allegations of sexual harassment.

The investigation's weaknesses included solicitation of anonymous complaints and no opportunity for mediation, Weir said, adding he's also concerned over subsequent statements by Singh about the investigation findings.

Weir was kicked out of the NDP caucus after the probe and was told he would not be allowed to run for the party.

"Regardless of what an external appeal may determine, I apologize to those who felt uncomfortable and will be more attentive in future," he said in a statement.

"What I do not accept is being expelled based on a single investigator's discretion without an appeal."

Singh is not backing away from his decision, saying he stands by the process.

"The investigation was a just and fair investigation," he said Wednesday after a caucus meeting.

Singh also said he hopes his decision will help address the "culture of silence" that exists on Parliament Hill.

"We all know on the Hill and in political parties ... that people have been discouraged from coming forward," he said.

"There's been a reluctance to talk about concerns. People haven't been able to voice legitimate claims of harassment."