Police say they arrested Saganash on June 27 in relation to an allegation from May 1 in Winnipeg and the matter is now before the courts.
He has not responded to a request for comment The Canadian Press sent by email on Friday, but APTN, which first broke the news, reports he confirmed the sexual-assault charge to them. The federal NDP has not responded to a request for comment.
Saganash had been one of the residential school survivors working with a national advisory committee for missing children and unmarked burials set up by the federal government and National Centre for Truth and Reconciliation in Winnipeg.
A spokesman for the centre said Saganash no longer holds that role, and did not say why or when he ended that position.
Saganash, A Cree lawyer, helped to negotiate the United Nations Declaration on the Rights of Indigenous Peoples. As an MP, he put forward proposed legislation to implement it in Canada.