From the Super Mario Wiki
Samantha Kelly (credited as Sam Kelly in some games) is Princess Peach and Toad's current and longest running voice actress, providing their voice work since Mario Strikers Charged and Mario Party 8 (excluding Mario & Sonic at the Olympic Games and Mario Kart Arcade GP DX). She also voices Toadette, Baby Peach and Pink Gold Peach.
Samantha Kelly was born in Kenya and has lived in the countries, Thailand, Laos, Vietnam and Germany. Prior to video games, she has done voiceover work for Nordstrom and other commercials. After Jen Taylor left the role of Princess Peach and Nicole Mills fill in as the temporary voice, an agent had Kelly audition for the role and was chosen.