He said the first challenge would be continuing cost-effective and efficient practices, and carrying on the hard work that had already been done by Bob Francis, the former chairman.
"Both DHBs are under the gun when it comes to expenditure," Mr Mark said.
"It will not be an easy task and that's what we will need to achieve."
Mr Mark said there would be a learning curve in his first year on the board but he had a background in health.
"Health is not new to me."
He is a patron of Maori mental health provider Te Awa o Te Ora Trust in Christchurch and was involved in establishing health initiatives during his time as a NZ First MP from 1996 to 2008.
"I was the person who drove the establishment of a cardiothoracic unit in Christchurch," he said.
Mr Mark is deputy chair of Wairarapa Moana Incorporation, as well as holding several other trustee and director roles.
Mr Milne has also been cross-appointed to deputy chair of Capital and Coast DHB.
Ms Southey is deputy chair for Wairarapa.
Mr Ryall said he made cross-appointments to encourage more regional collaboration in planning and delivering health services.
"For example, there are multiple cross-appointments of chairs and deputies in the four Northern region boards and the three boards in the Greater Wellington region," he said.
"It makes good sense to have some members on neighbouring boards, as there are overlaps in care provided to patients," Mr Ryall said.
"Capital & Coast DHB, for instance, provides nearly 35 per cent of Hutt Valley's elective surgery."
Mr Mark said he had worked closely with Mr Ryall and said he was one of the most competent ministers in the Government.
"I worked with Tony Ryall both when we worked in Government together and opposition together in 2002 to 2005.
"We worked very closely together on law and order."
The minister appoints four members of the DHB, who start on December 9, and the public elected seven in October in the local body elections.
Last Friday, Mr Ryall announced seven chair and deputy chair cross-appointments to New Zealand's 20 DHBs.