He will split his time evenly between Invercargill and Dunedin, a spokesman said.
Mr Tulloch's appointment means the end of separate officers for Otago and Southland.
Former Otago CMO Dick Bunton has been appointed patient services medical director, focused on operational day-to-day medical matters, while Mr Tulloch's role was strategic and high-level, a spokesman said.
Mr Bunton remains at executive level, in a change to the new structure announced in June.
The restructuring resulted in the loss of one from the top table, from 13 members to 12.
"I am pleased to have two high-calibre senior clinicians in these roles as we continue our journey to becoming a more unified, high-performing, patient-centred district health board," chief executive Carole Heatly told staff yesterday.
Mr Tulloch would work as the principal medical adviser to the board and executive, and work closely with the Ministry of Health and National Health Board, she said, in a press release.
