Bishop Desmond Tutu resigned as Bishop of Lesotho Anglican Church after being appointed as the first Black Secretary-General of the South African Council of Churches (SACC). The choice of Tutu for the position was influenced by the increasingly critical position the SACC was taking in its fight against Apartheid. 

References:

South African History Online http://mzansiafrika.typepad.com/mzansi_afrika/sadc/index.html http://www.achievement.org/autodoc/page/tut0bio-1