"Kelly brings a unique blend of technology, commercial and management expertise from a career spanning financial services, management consulting and the Silicon Valley tech sector to Optus," said Singtel group chief executive Chua Sock Koong.
"She will build on the success of Optus that has flourished under Allen's dynamic leadership, particularly as we move into the next phase of 5G-powered growth."
Departing chief executive Allen Lew said "I look forward to passing the baton to Kelly whose ability to leverage technology, data and analytics to develop leading customer services and experiences will ensure Optus stays ahead of the game."
"I'm eager to work more closely with the AIS team to strengthen their leadership in the exciting Thai market," he said.
Chua said: "Allen's standout tenure at Optus has made it the go-to operator in Australia for great connectivity, innovative services and exciting content. Given the tremendous growth of digital services in Thailand and the
strides taken by AIS to assert market leadership, he is best placed to help drive growth there given his knowledge of the Thai market and expertise."
Prior to joining Singtel in March 2019 as deputy chief executive, Bayer Rosmarin spent 14 years at the Commonwealth Bank where she held a number of management positions, most recently that of group executive of institutional banking and markets. Earlier in her career she worked as a consultant at the Boston Consulting Group, as director of CRM sales product management at PeopleSoft (now part of Oracle), in corporate development at Calico Commerce.
She is a special adviser to the University of New South Wales' engineering faculty, special advisor the the NSW Government, a member of the federal Department of Finance's fintech advisory group, and a director of the Football Federation Australia.
Bayer Rosmarin holds a bachelor's degree in industrial engineering and a master's in management science and industrial engineering, both from Stanford University.