Born Timothy Ware in Bath, Somerset, England, he was educated at Westminster School in London (to which he had won a King's Scholarship) and Magdalen College, Oxford, where he took a double first in classics as well as reading theology. On 14 April 1958, at the age of 24, he embraced the Orthodox Christian faith (having been raised Anglican), travelling subsequently throughout Greece and spending a great deal of time at the Monastery of Saint John the Theologian in Patmos. He also frequented other major centres of Orthodoxy such as Jerusalem and Mount Athos. In 1966 he was ordained to the priesthood and was tonsured as a monk, receiving the name Kallistos.

In 1966 Ware became a Spalding Lecturer at the University of Oxford in Eastern Orthodox studies, a position he held for 35 years until his retirement. In 1979 he was appointed to a Fellowship at Pembroke College, Oxford, and in 1982 he was consecrated to the episcopacy as an auxiliary bishop with the title Bishop of Diokleia, appointed to serve as the assistant to the bishop of the Ecumenical Patriarchate's Archdiocese of Thyateira and Great Britain. Despite his consecration, Ware remained in Oxford and carried on his duties both as the parish priest of the Greek Orthodox community and also as a lecturer at the university.

Since his retirement in 2001, Ware has continued to publish and to give lectures on Orthodox Christianity. He was previously the chairman of the board of directors of the Institute for Orthodox Christian Studies in Cambridge. He is the chairman of the group Friends of Orthodoxy on Iona and of the Friends of Mount Athos.

On 30 March 2007 the Holy Synod of the Ecumenical Patriarchate elevated the Diocese of Diokleia to a metropolitan diocese and thus Ware became a titular metropolitan even though he has never had pastoral care of any diocese and is nominally an assistant bishop in the Archdiocese of Thyateira and Great Britain.

Ware is perhaps best known as the author of the book The Orthodox Church, published when he was a layman in 1963 and subsequently revised several times. More recently he produced a companion volume, The Orthodox Way. But his most substantial publications have emerged from his translation work. Together with G. E. Palmer and Philip Sherrard he has undertaken to translate the Philokalia (four volumes of five published to date, but no progress has been made with the fifth volume for sixteen years now); and with Mother Mary he produced the Lenten Triodion and Festal Menaion.

• The Orthodox Church, 2nd ed. (Pelican, 1993 ISBN 0-14-014656-3)
• The Orthodox Way (St Vladimir's Seminary Press, 1995, ISBN 0-913836-58-3)
• The Lenten Triodion, Tr. Mother Mary and Archimandrite Kallistos Ware (St. Tikhon's Seminary Press, 2002, ISBN 1-878997-51-3) - first published by Faber and Faber Ltd., 1978
• The Inner Kingdom: Collected Works, Vol. 1 (St Vladimir's Seminary Press, 2000, ISBN 0-88141-209-0)
• In the Image of the Trinity: Collected Works, Vol. 2 (St Vladimir's Seminary Press, 2006, ISBN 0-88141-225-2)
• Communion and Intercommunion (Light & Life, 1980, ISBN 0-937032-20-4)
• How Are We Saved?: The Understanding of Salvation in the Orthodox Tradition (Light & Life, 1996, ISBN 1-880971-22-4)
• Praying with Orthodox Tradition (Abingdon, 1990, ISBN 0-281-04431-7)
• Eustratios Argenti: A Study of the Greek Church under Turkish Rule (Clarendon, 1964, ASIN B0006BMI94)

He has also co-authored, edited and translated many other works.