"There's something rather comforting about being in this position, given I signed my resignation about half an hour ago,'' Mr Key said.
Speaking to reporters following the ceremony, Mr Key said Cabinet would meet at about 2pm, and a second meeting would be held on Monday before the Christmas break.
Mr Key said the Government's plan to sell shares in state assets would be among the issues on the agenda for the first meeting, and that there was some early advice around the timeframe and work programme for the plan.
"We won't be making further decisions on that today, but there is some preliminary advice."
Mr Key said there was a great degree of expectation on the new Government, and that his ministers had been warned about that.
"It's an encouraging message as opposed to a threatening one,'' he said.
"I believe we've got together the best ministry we can with the best people that are dedicated to what they are doing.''