Dr Lang is widely regarded as having established Parramatta City Council as a leader in local government and helped reposition the City for future growth.
He joined Council in July 2008 and said he was proud of the organisation's many achievements over the past five years and would take with him plenty of fond memories.
"The decision to move on from Council was not an easy one, and while it is sad to leave behind many valued colleagues and councillors, I feel satisfied with what we as an organisation, and City, have been able to achieve," he said.
"I will always look back at my time with Council as special, and I look forward to watching the development of Parramatta continue on its rapid ascent." Parramatta Lord Mayor.
Cr John Chedid, praised the CEO's dedication, confirming that Dr Lang had realised many of the short and long-term objectives during his tenure, specifically the commencement of Parramatta Square.
"Parramatta Square, or Civic Place as it was once known, has been the biggest project we've ever faced as a Council and Dr Lang played a key role in ensuring its delivery," Cr Chedid said.
"Dr Lang was also instrumental in creating a new operations centre for Council, which is about to start construction at Rydalmere, and has also passionately lobbied for improved infrastructure to support the future growth of Parramatta.
"Council is much stronger financially, continually exceeds best practice local government benchmarks and has a high level of staff engagement. These achievements can be attributed to the efforts, dedication and vision of Dr Lang.
"On behalf of myself, the organisation and fellow councillors, I'd like to thank Dr Lang for his commitment to Council and wish him, his wife Annette and family, the very best of luck in the future."
Dr Lang's resignation will take effect on January 2, 2014. His last day at Council will be October 25 2013, having already pre-organised an overseas holiday with his family.
Council will soon start an executive search for Dr Lang's replacement and expects to have it finalised by the end of the year.
