The 12-hour vigil was held at St Martin in the Fields church and was attended by the Bishop of London, Dr Richard Chartres, and the Archbishop of Westminster Vincent Nichols.
It also marked the start of the Olympic Truce 50 days before the start of the Games in London.
The tradition of a truce before the Olympics goes back thousands of years to Ancient Greece when it guaranteed the safe passage of competitors and visitors to the competition.
The vigil was organised by Westminster Justice and Peace, with St Martin in the Fields and the London Church Leaders' Group.
Faith groups were invited to pray over 100 days for peace in the capital, and to build a peace legacy for London after the Olympic Truce ends on 28 October.
Singer and hymn writer Graham Kendrick was among the musicians who performed at the church vigil.
Each hour of the vigil was led by a different group, including Ethelburga's Centre for Peace and Reconciliation, More Than Gold, London Citizens and World Vision.