After five years at Sasol, Tienie completed an MBA before joining Sanlam Investments in 1990. He held various positions in equity research and portfolio management before becoming the Chief Executive of Gensec Private Clients, renamed Sanlam Private Clients in 1998. In this role, Tienie led the acquisition of businesses from ANB Amro and Merrill Lynch.
In 2004, Tienie was appointed Chief Executive of Sanlam Collective Investments. He was part of the Sanlam team that assessed investment opportunities in India. In 2009, he relocated to India to become the Chief Executive of SMC Global, a wealth and asset management joint venture between Sanlam and SMC India. Tienie returned to South Africa in late 2011 and joined Ora as a non-executive director on 1 February 2012 and is also the Chairman of the Ora Audit and Risk Committee. He is the Non-executive Chairman of H4, the CIS Manco in the Citadel Group, and Non-executive Chairman of CI Collective Investments an associated company in the Analytics group. Tienie also serves as a non-executive director of TBI Strategic Partners and Sasfin Financial Services.