He was superintendent of the Methodist (later Uniting Church in Australia) Wesley Mission, Pitt Street, Sydney, 1958–1978 and one of the founders of the National Christian Youth Convention (NCYC) in 1955 and Lifeline in 1963.

He was involved in founding the World Methodist Evangelism Institute (located at the United Methodist-related Candler School of Theology at Emory University) in Atlanta, 1982.

Walker launched Lifeline in Sydney, Australia in 1963 after a call from a distressed man who three days later killed himself.

Lifeline Sydney was two years in planning and preparation, with 150 people attending a nine-month training course to work at the Centre.

A century old, dilapidated building owned by the Mission, on the fringes of downtown Sydney was renovated for the purposes of this new support centre.