WASHINGTON — Vice President Mike Pence will speak on Friday to a gathering of anti-abortion activists on the National Mall, a sign of the movement’s new and growing authority in a government now dominated by Republicans.

The organizers for the event, the March for Life, had extended invitations to President Trump and Mr. Pence. A senior White House official confirmed that Mr. Pence would address the marchers.

Mr. Pence’s appearance will come just a few days before Mr. Trump is expected to reveal his nominee for the Supreme Court seat left vacant by the death of Justice Antonin Scalia last year. Mr. Trump has said his pick, like Mr. Scalia, would oppose abortion rights, one of several promises he has made to roll back legal protections for the procedure.