Sarah Geronimo was born on July 25, 1988 in Santa Cruz, Manila, Philippines, to Delfin Geronimo, a retired Philippine Long Distance Telephone Company (PLDT) employee, and Divina Geronimo, who ran a beauty parlor from the family home.
She studied at Dominican School Manila. Geronimo’s first performance was in a mall show when she was two years old. At the age of four, she made her first appearance on national television and was a member of the children's television show Pen-Pen de Sarapen for two years.
At six, she performed at a short concert at Isetann Cinema Complex on Recto Avenue in Manila. She sang for Pope John Paul II during his visit to the Philippines in 1995, when she was six. At the age of eight, her father enrolled Geronimo at the Center for Pop Music Philippines, where she received her first formal music and voice lessons. Geronimo performed in hotel lounges, on campuses, in shopping malls, and on a few TV shows. Around this time, she was part of the cast of the ABS-CBN children's show Ang TV. At the age of nine, she joined the cast of the TV show NEXT. She also played a cameo role in Star Cinema’s Sarah, Ang Munting Prinsesa.