Agbayani was born on July 2, 1961 to a Roman Catholic family. She studied high school at the University of Santo Tomas before enrolling in the University's Bachelor of Science in Architecture program in 1979. She eventually dropped from the program due to showbiz commitments.

In the United States, Agbayani was able to pursue acting in Hollywood. She appeared in international productions, sometimes credited as Carol Roberts. Her films include John Boorman's The Emerald Forest (1985); a cameo in The Money Pit (1986); leading lady in Gymkata (1985); and as a Geologist in the Australian film Rikky and Pete (1988). Agbayani also appeared in an episode of the British television series Yellowthread Street.

In 1989, Agbayani returned to the Philippines and took time out from her career to give birth to her daughter, China. During this period, Agbayani devoted her whole time as a mother, living a quiet, private life for several years.

In 1995, Agbayani resumed her education and enrolled in Saint Joseph's College, Quezon City. She graduated with a Bachelor of Science in psychology in 2000. In 2001, she was accepted into the Master of Arts in psychology with a concentration in counseling psychology program at Ateneo de Manila University. She completed all academic requirements and is now working on her master's thesis. She is also teaching psychology at Saint Joseph's, while doing occasional TV and film appearances.