WASHINGTON — Vice President Harris has chosen Governor Walz of Minnesota as her running mate, CNN is reporting, and she will campaign with him at a rally Tuesday evening at Philadelphia.

In recent days, she had zeroed in on a trio of potential finalists: Governor Shapiro of Pennsylvania, Senator Kelly of Arizona, and Mr. Walz.

Ms. Harris’ campaign plans to make the announcement via video message before the rally, though the exact timing remained unclear, according to a person involved in the planning who spoke on the condition of anonymity to detail discussions occurring behind closed doors.

Doing so would be similar to how President Biden, then a candidate, announced Ms. Harris as his vice presidential choice during the pandemic-marred presidential race of 2020.

It will mark be another milestone in the barely two weeks since the vice president moved to take over the top of the Democratic ticket heading into November’s election.

She has been scrambling to build out a campaign since then and to breathe new life into the Democratic race against President Trump.