He said he looked forward to coming up to speed with the demands of his ministerial portfolios.
"It will mean the intensity here will increase but it won't pull me away from the electorate," he said.
"I pride myself on being part of the community I represent and will work extra hard to make sure that continues."
After almost five years in Parliament, Mr McClay's long-term goal as a politician was to continue representing Rotorua.
"I have only ever wanted to be a constituency MP," he said.
"In five years' time I still want to be representing Rotorua and working with local people."
One of Mr McClay's first jobs in his new ministerial position will be taking over the Psychoactive Substances Bill - regulating legal highs such as synthetic marijuana.
"Ensuring that our legislation provides the right safeguards against these unregulated substances will be an early priority for me."
As part of his promotion, Mr McClay receives a pay increase, a bigger office in Parliament and additional staff to help him deal with his ministerial responsibilities.
According to the New Zealand Parliament website, his annual pay has increased from $155,700, as a chairperson of a select committee, to $217,200 as a minister outside the Cabinet.
He said he found out he had been handed the ministerial position when Mr Key rang him on Sunday.
"The Prime Minister called me on Sunday afternoon. I was actually with my family at a Korean church we had been invited to attend in Rotorua."
Lakes District Health Board chairman Deryck Shaw said it was good news for Rotorua with Mr McClay picking up the Associate Minister of Health duties: "He has always taken interest in health outcomes in our district. I think it is good news for Rotorua."
Mr Dunne resigned as a minister last week after refusing to provide emails to an inquiry into the leak of a report on the GCSB, although he denies he was responsible for the leak.