Bishop John Walker was born in Georgia in 1927, but spent his early years in Detroit, Michigan. He received his Bachelor of Arts degree from Wayne State University in 1951 and was the first African American to attend Virginia Theological Seminary, where he completed his Bachelors of Divinity in 1954.

Bishop Walker was ordained a deacon in 1954. After his ordination to the priesthood the following year, he became rector at St. Mary's in Detroit. In 1957, he joined the teaching staff at St. Paul's School in Concord, New Hampshire, where he served until 1966 when he was elected Canon of the Washington National Cathedral. During the 1964 to 1965 school year, he took a leave of absence from St. Paul's to teach at the Bishop Tucker Theological College in Uganda. From 1960 to 1966, he served on the Advisory Committee on Civil Rights, which studied the problems of discrimination in reference to race, religion, and national origin.

While serving the as Canon at the Cathedral in Washington, D.C., Bishop Walker not only participated in services and preached, but he also concentrated on the Cathedral's specialized ministry to the D.C. community. In 1971, he was consecrated as Suffragan Bishop of Washington, a position he held until 1976 when he was elected Bishop Coadjutor. The next year he was installed as the nation's second Black diocesan bishop when he was consecrated Bishop of Washington. He began his service as Dean of Washington Cathedral in 1978 and was a candidate for Presiding Bishop in 1985.

Walker led his community in multiple roles within and outside of the church. He was a member of the Joint Standing Commission on Ecumenical Relations (1974-1978), the Joint Commission on the Church in Metropolitan Areas (1980-1982), the Standing Commission on Peace (1986-1989), the Consultation on Church Union, and the Urban Bishops Coalition. In 1975, he served as a delegate to the World Council of Churches. He was elected vice president of the House of Bishops in 1987. From 1975 until his death in 1989, he was president of the Board of Directors of Africare, an aid organization focused on community development in sub-Saharan Africa. As a close friend of South Africa's Archbishop Desmond Tutu, he exercised effective leadership in the church's opposition to apartheid.

Bishop Walker's papers are housed at the Diocese of Washington and the National Cathedral of St. Peter and St. Paul.