Cartwright was born in Dayton, Ohio, on October 25, 1957, Frank and Miriam Cartwright's fourth of six children. She grew up in Kettering, Ohio, and discovered her talent for voices at an early age. While in the fourth grade at the school of St. Charles Borromeo, she won a school-wide speech competition with her performance of Rudyard Kipling's How the Camel Got His Hump. Cartwright attended Fairmont West High School, and participated in the school's theater and marching band. She regularly entered public speaking competitions, placing first in the "Humorous Interpretation" category at the National District Tournament two years running. The judges often suggested to her that she should perform cartoon voices. Cartwright graduated from high school in 1976 and accepted a scholarship from Ohio University. She continued to compete in public speaking competitions; during her sophomore year, she placed fifth in the National Speech Tournament's exposition category with her speech "The Art of Animation".