Walls was born in 1928 in New Milton, England. He studied theology at Exeter College, Oxford, receiving a first-class degree in 1948, and completed his graduate studies in the early Church in 1956 under the patristics scholar Frank Leslie Cross.
He taught at Fourah Bay College, Sierra Leone (1957–62) and the University of Nigeria, Nsukka (1962–65). He was later appointed to a post in ecclesiastical history in the University of Aberdeen in 1966, before being the first head of the Department of Religious Studies in the University of Aberdeen (1970). He would subsequently move to the University of Edinburgh in 1986. He is currently Professor of the History of Mission at Liverpool Hope University, Honorary Professor at the University of Edinburgh, Research Professor at Africa International University's Center for World Christianity, and Professor Emeritus at the Akrofi-Christaller Institute of Theology, Mission and Culture.
Walls established the Journal of Religion in Africa in 1967 and Studies in World Christianity in 1995. He also founded the Centre for the Study of World Christianity, first at the University of Aberdeen in 1982, before moving it to the University of Edinburgh in 1987, a year after he moved to Edinburgh.
With his late wife Doreen Harden, whom he married in 1953, they have two children, Christine and Andrew. After Doreen's death, he married Ingrid Reneau in 2012, a Research Fellow with the Presbyterian Mission Agency.
Walls' most significant observations have concerned the geographical trends in Christianity in the 20th and 21st centuries, especially in terms of expansion in Africa, in what is generally termed World Christianity. Historian Lamin Sanneh commented that he was 'one of the few scholars who saw that African Christianity was not just an exotic, curious phenomenon in an obscure part of the world, but that African Christianity might be the shape of things to come'. His pioneering research led the magazine Christianity Today to describe him in 2007 as 'a historian ahead of his time' and 'the most important person you don’t know'.
Liverpool Hope University has a research centre named in honour of him, which encourages and supports research in the field of African and Asian Christianity.
Although he is more well known for his work in Christianity, Walls has also been a significant pioneer in shaping the field of religious studies as it is taught in universities of Scotland. When he first returned to Scotland, Walls taught Ecclesiastical History in the University of Aberdeen in 1966. However, he recognized that the Faculty of Divinity in Aberdeen did not allow for a sufficient global perspective of religion, and founded the Department of Religious Studies outside the Faculty of Divinity in 1970.
Significantly, Walls' work in Aberdeen would establish the first department of Religious Studies in Scotland. In the mid-1970s, the department would be known for emphasising work in the study of what was then called 'primal religions'. Moreover, his vision for a global perspective of religion allowed for Walls to attract a number of significant members of staff and students who were interested in religions of the non-Western world. It would also be in this new department that the original Centre for the Study of Christianity in the Non-Western World was established, before eventually being relocated to the University of Edinburgh in 1987.Walls, Andrew Finlay (1996). The Missionary Movement in Christian History. Maryknoll, NY: Orbis Books. ISBN 978-1-570-75059-5. OCLC 33948470.
——— (2002). The Cross-Cultural Process in Christian History: Studies in the Transmission and Appropriation of Faith. Maryknoll, NY: Orbis Books. ISBN 978-1-570-75373-2. OCLC 47237613.
———; Ross, Cathy (2008). Mission in the Twenty-First Century: exploring the five marks of global mission. Maryknoll, NY: Orbis Books. ISBN 978-1-570-75773-0. OCLC 173243828.
———; Shenk, Wilbert R., eds. (1990). Exploring New Religious Movements: essays in honour of Harold W. Turner. Elkhart, IN: Mission Focus. ISBN 978-1-877-73608-7. OCLC 22281800.
———; Fyfe, Christopher, eds. (1996). Christianity in Africa in the 1990s. Edinburgh: Centre of African Studies, University of Edinburgh. OCLC 35318556.
Walls, Andrew Finlay (1959). "Introduction". The First Epistle General of Peter. Tyndale New Testament Commentaries. Tyndale Press. ISBN 978-0-851-11813-0. OCLC 978540.
Full bibliography of works can be found in William Burrows, Mark Gornik and Janice McLean (eds) Understanding World Christianity: The Vision and Work of Andrew F. Walls (Maryknoll, New York: Orbis Books, 2011).