In 1990, Rennis was ordained as a deacon at St Andrew's Cathedral and on 1991, he was ordained as a priest. On 4 May 2005, he was consecrated as the Assistant Bishop of Singapore. Prior to becoming the Bishop of Singapore, he was Vicar of St John's - St Margarets' Church.
- "Rennis Ponniah to be installed as the 9th Bishop of Singapore on 20th October 2012". Global South Anglican. 1 July 2012. Retrieved 29 September 2012.