One of six children of the late Gerald and Beatrice (Morin) Callahan, Father Callahan was born in Lawrence on Sept. 2, 1952. He grew up initially in North Andover, and then in the "Immigrant City," Lawrence, in St. Patrick Parish. The parish school, which young David attended, had been staffed since its founding by the Sisters of Charity of Halifax. The parish gave sons and daughters to religious and priestly vocations in enviable numbers.

He was a high school student at Lawrence's Central Catholic High School before his undergraduate studies at Merrimack College, North Andover. He returned home to Lawrence and his alma mater, and for seven years, taught middle school at St. Patrick.

He entered St. John Seminary, Brighton, and following his seminary formation, he was ordained at Holy Cross Cathedral on June 20, 1987, by Bernard Cardinal Law. The cardinal gave him his first assignment as a parochial vicar at Sacred Heart Parish, Weymouth.

In 1993, he was parochial vicar at St. Mary of the Annunciation, Melrose.

Cardinal Law tapped him to be pastor of St. Anne Parish, Littleton, naming him on June 6, 1998. Archbishop Seán P. O'Malley named him pastor of St. Mary Parish, Franklin, on June 1, 2005; and three years later, he was named pastor at St. Mary Parish, Quincy.

When he was first named a pastor, he told The Pilot that he hoped "he could be a pastor to everyone." "Being a happy priest and that being obvious to parishioners" was his very effective way of fulfilling that hope.

After almost 17 years as pastor in three large parishes, in 2014, he went back to being a parochial vicar and started back at familiar territory: Weymouth. He was parochial vicar back at Sacred Heart, Weymouth, and at St. Thomas More, Braintree, serving at both from 2014 to 2017.

In 2017, he was facing north again and was now parochial vicar at three parishes in Somerville: St. Joseph, St. Ann, and St. Catherine of Genoa. The three parishes worked together in 2019, as the three became one with the creation of Sts. Louis and Zelie Martin Parish. He served as administrator of the new parish for six months, between February and August 2023, returning to his recently achieved status as parochial vicar of the new parish and remaining until June 1, 2026, when Archbishop Richard G. Henning granted him senior/priest retirement status.

Father Callahan indeed is a happy priest. With a dry sense of humor, he offered insightful commentary on issues and matters civic and ecclesiastical, but always generously and kindly.

In his retirement, Father Callahan will live in his own residence in Maine.