David Perez, a retired medical oncologist and former chairman of the new Dunedin Hospital design clinical leadership group, will be joined by former nurse and Canterbury DHB chief executive Jean O'Callaghan on the commissioner team.
Commissioners can appoint deputies at their discretion.
Richard Thomson is currently the sole deputy to Mrs Grant after the sudden death of Graham Crombie in February.
''We continue to feel the loss of Graham, and he cannot be replaced,'' Mrs Grant said.
''However, David's greatly respected clinical voice and decades of experience at Southern, along with Jean's wealth of international organisational and healthcare experience, provide us with enormously valuable expertise and I am grateful for their willingness to step into these roles.''
Mrs Grant said she had already decided she needed to appoint a deputy commissioner with a clinical focus, and the loss of Mr Crombie led to her decision to enlist two new deputies.
''Graham's passing sadly interrupted this planning, and it became necessary to look more broadly at the skills needed across the team over this crucial period,'' she said.
The Southern District Health Board was replaced by a commissioner in 2015 because of progressively worsening deficits.
The SDHB deficit was forecast to reach $27million at that point, a figure projected to grow to between $30million and $42million.
As at December 31 last year, the SDHB's year-to-date deficit was $25.9million, $8.3million more than budgeted.
The SDHB has predicted its deficit will fall in future years, but has also warned its ability to return to surplus was ''significantly challenged'' by rising costs, particularly in pharmaceuticals.
Legislation ordering the commissioner appointment at the SDHB requires an elected board to resume control from this year's local body elections.
The election is scheduled for October; the new board will formally assume its role in December.
''We are entering the final phase of our term as a commissioner team,'' Mrs Grant said.
''We are keenly focused on making sure the strategic developments and improvements that have been made are secure and able to be handed over successfully to the incoming board.''
