Final results showed that National Party won 45 per cent of the vote, giving it 59 seats in the 122-seat parliament.
The ACT party, an ally, won five seats to ensure a National-led coalition, while the centrist United Future Party, also friendly to National, took one seat.
"I can confirm their willingness to lend support to establishing a new government in New Zealand," Key said.
Key will not need the support of the indigenous Maori Party, which won five seats.
The Labour Party took 34 per cent of the vote, giving it 43 seats, while its allies, the Green Party, had six per cent of the vote, enough to secure eight seats.
Key, a 47-year-old multi-millionaire former foreign currency trader, campaigned at a time of domestic recession and global financial crisis.
For her part, Clark had urged voters not to change governments, saying that the New Zealand needed consistent leadership during a time of economic uncertainty.
Her party accused Key of stealing its policies and of having a hidden right-wing agenda.
Earlier, Anthony Green, a political analyst, told Al Jazeera: "Key, a self-made millionaire financier, has played on [the flailing economy], promising a better economy.
"The weather in New Zealand tends to be more fickle than the politics - four seasons in one day is not an uncommon experience. But if the pundits and the pollsters are right, New Zealand will vote for change and, unlike America, opt for the conservatives."