"We have anticipated that there could be an earlier election and more so given the change of leadership in the National Party.
"So I think I'd probably rather avoid a by-election and just get straight into an earlier election."
Shearer is poised to resign from Parliament to take up the tough job of leading the United Nations' mission in war-torn South Sudan.
Little said he heard from Shearer two weeks ago that he had been offered the role at the UN and that he wanted to accept it.
"We are very excited for him," said Little.
"Should he be confirmed, David will be the only New Zealander in charge of a UN peacekeeping mission. This is a very exciting opportunity for him to make a difference and help bring peace to a country of nine million people torn apart by civil war.
"We fully understand his reasons. This is a once-in-a-lifetime opportunity to take up a senior position at the United Nations which reports directly to the Secretary-General."
Shearer's resignation will mean a byelection in his Mt Albert electorate early next year, the first electoral challenge for the new Prime Minister.
Little said there had been no thought about who should run in the Mt Albert seat for Labour in place of Shearer, but people would be queuing up.
Shearer said this morning the Security Council would be making a decision on his post.
"There has been a high degree of media interest in New Zealand about a possible post with the United Nations," he said.
"My name has been proposed to the United Nations Secretary-General to be his special representative in South Sudan.
"The matter is currently before the Security Council for its decision.
"Until the Council completes its consideration of the appointment I will not be commenting further."
Little said the Special Representative and head of the United Nations Mission in South Sudan (Unmiss), is regarded as "the most challenging of peacekeeping operations currently".
Unmiss is the UN's third-largest peacekeeping mission with 17,000 uniformed and almost 2000 civilian personnel. It is charged with building peace and stability in what is the youngest country in the world.
The appointment is a personal one by the UN Secretary-General. It does not require a nomination by the Government.
But Foreign Affairs Minister Murray McCully said Shearer, who is Labour's foreign affairs spokesman, had the strong support of the Government.
"It is a huge deal," he said.
"[Security Council members have] a couple of days to raise any concerns, so it is not a done deal yet.
"But it is a big feather in his cap.
"This is the toughest peace-keeping assignment on the planet. It is a difficult and dangerous place."
