Thwaites will manage three GNN regions - London, the South-East and the East - covering Portsmouth to Norfolk, overseeing 35 press officers and administration staff.
Its network of ten press offices managed an internet press centre and regional government comms, making policy relevant locally, said a spokesman.
Thwaites spent three years at the Government's 24-hour media monitoring unit and was previously editor at BBC London Online. She is also a former Thames Valley FM news editor, BBC Greater London Radio breakfast editor, and BBC Newsroom Southeast output editor.
Thwaites will report to GNN director Rob Haslam and takes over from Virginia Burdon, who recently retired.