Opposition politicians and others have claimed, without evidence, that Mr. Trudeau demoted Ms. Wilson-Raybould to the veterans affairs job, a less prominent position, as punishment last month.

“When I sought elected office it was with the goal of implementing a positive and progressive vision of change on behalf of Canadians,” Ms. Wilson-Raybould, who will remain a Liberal member of Parliament, said in her resignation letter. She said her resignation from the cabinet “in no way changes my commitment to seeing that change achieved.”

Speaking with reporters in Winnipeg, Manitoba, Mr. Trudeau said that “to be honest, I don’t entirely understand why Jody Wilson-Raybould made the decision she did.” He said that she had never raised concerns with him that she was being improperly pressured, either in recent conversations or last fall, when the incidents are supposed to have occurred.

Mr. Trudeau dismissed the idea that the government had acted improperly toward Ms. Wilson-Raybould. He said that if it had done so, “it was her responsibility to come forward to me this last fall and highlight that to me. She did not.”

He added, “We followed all the rules and standards.”

Alluding to the ethics questions, Ms. Wilson-Raybould said in her letter that she had retained Thomas Albert Cromwell, a former Supreme Court justice, for legal advice on what she can reveal about her conversations about SNC-Lavalin. Mr. Trudeau has separately asked her successor to look into whether privilege can be waived.