Sears was born in Alton, Illinois. His own father deserted the family, so one of his primary male adult influences was his grandfather.

Sears' residencies were taken at Children's Hospital Boston and the Hospital for Sick Children in Toronto. He is an Associate Clinical Professor of Pediatrics at the University of California, Irvine, School of Medicine. FOXNews.com - Asthma Out of Control in America's Kids - Health News | Current Health News | Medical News

He is a medical and parenting consultant for BabyTalk and Parenting magazines and the pediatrician on the website Parenting.com According to his biography, he has been a guest on more than 100 television shows including: 20/20, Donahue, Good Morning America, Oprah Winfrey, CBS This Morning, CNN, Today Show and Dateline.

According to his website, in 1997, Sears underwent major surgery for colon cancer, followed by radiation therapy and chemotherapy.

Sears and his wife Martha have eight children, one of whom has Down's Syndrome. Three of the children have also become doctors, Jim the oldest (The Doctors), Bob (second oldest), and Pete. A fourth son, Matt, is currently studying medicine at UC Irvine.

Sears and several of his family members are distributors and spokespersons for Juice Plus dietary suppplements, which Sears promotes on his website. AskDrSears.com - Juice Plus+ National Safety Associates (NSA), the company that markets Juice Plus, used testimonials from Bill Sears in advertisements promoting Juice Plus Gummies. Juice Plus+ "is the next best thing to fruits and vegetables”.

As of 2009, Sears lives with his family in San Clemente, California, and operates a private medical practice (Sears Family Pediatrics) in Capistrano Beach, California with his sons.