His vision included "creating a clean, green and clever New Zealand and an economy that delivers benefits to all New Zealanders".
Mr Shearer urged Prime Minister John Key to open a proposed ministerial committee on poverty-related issues to all political parties.
"I want to be on it and to have the chance to offer my expertise to help us deal with the problem. I have seen the world at its worst and I want the best for New Zealand."
In 2002 Mr Shearer lost a lunge at the Whangarei seat. His campaign was foiled by his own party calling an early election - he was still at his UN post in Afghanistan when the election began. Despite the late start, his loss by 3214 votes to incumbent MP Phil Heatley was closer than many expected.
His credentials include managing aid programmes in war-torn and third-world countries, including Iraq, Somalia, Kosovo and Afghanistan for the UN and other organisations. He was an adviser to then Foreign Affairs Minister Phil Goff. He had also taken a late run at the 1999 election, where he was bottom of the party list.
The secret ballot that gave him the leadership followed the tight "Two Davids" race against David Cunliffe. A week was a long time in politics, and "the last two weeks have felt like a lifetime," Mr Shearer said.
His most recent party roles have been MP for Mt Albert and spokesman for Tertiary Education, Research and Development, and Science and Technology.
He was New Zealander of the Year in 1993 for his aid work in Somalia, and made an MBE (Member of the British Empire) that year. In 1994 he received Save the Children's international award for gallantry.