Reverend Middlebrook has had a long career in the civil rights movement starting in the early 60s when he was a student at Morehouse. 

He served as the youth minister at Ebenezer Baptist Church in Atlanta, where both King and his father held pastorates. He was also a member of the Student Nonviolent Coordinating Committee (SNCC) and participated in several sit-ins in Atlanta.

In 1968, as assistant pastor to Rev. Benjamin Hooks at Middle Baptist Church in Memphis, Middlebrook served on the strategy committee of the Community on the Move for Equality (COME), where he organized youth activities.

He held pastorates in Greater Springfield Baptist Church in Bolivar, Tennessee, from 1970 to 1977, and Mount Calvary Baptist Church in Knoxville, Tennessee, beginning in 1977. He also served as director of Christian education for the West Tennessee Central Baptist Association, and as president of the Hardeman County Ministerial Association.

In 1980, Reverend Middlebrook became the founding pastor of Canaan Baptist Church of Christ, Inc. He has faithfully served the Canaan family and remained active in the community for over 4 decades, even returning to serve after a short retirement.