One of the five children of Joan (Cushing) Sullivan, and the late James, Timothy was born in Weymouth on July 19, 1958. His older sister, Joan Foley, and a younger brother, James, are deceased; he has two younger sisters: Susan McBride and Ellen Burns.

Married to Joyce (Nagle) Sullivan, they are the parents of Timothy, who lives in Weymouth. He and his wife are parishioners of St. Francis of Assisi Parish, Braintree.

He was raised in Braintree and attended local public schools Donald E. Ross Elementary and Archie T. Morrison Elementary, then East Junior High and Braintree High School.

With a lengthy career in education, he has degrees in elementary education from Barrington College, Barrington, R.I.; Eastern Nazarene College, master of education in reading education; Bridgewater State University, CAGS in school administration; and, from the University of Massachusetts-Lowell, a doctorate in education specializing in school leadership.

He has been an elementary school teacher in Brockton as well as a reading specialist. He is a member of the Massachusetts Teachers Association and has served on several boards and commissions.

During his diaconal formation, he has served at South Shore Hospital, Weymouth; and at various ministries at both St. Francis of Assisi and St. Clare Parishes in Braintree.