On a whim, today I decided to look up the voice actor behind the Valorant announcer. Turns out her name is Cynthia Kaye McWilliams (IMDb link) and she's been in a fair number of video games, including Far Cry New Dawn, inFamous: Second Son, Halo 5, and - you guessed it - League of Legends.

In League of Legends, she voices Senna. So it's Senna announcing when you get an Ace or Clutch. Take that as you will. ;)