Fillebrown was born in Winthrop, Maine. Fillebrown was a dentist and for many years a professor of dentristry at Harvard University from 1883-1904. He was a successful oral surgeon and performed many operations to fix cleft pallets. Fillebrown held a degree in dentistry from Harvard and a medical degree from Bowdoin College. At the time of his death Fillebrown was serving as president of the American Academy of Dental Science.