"We have to be relentlessly outward-looking."
The economist moved to New Zealand from Scotland in 1988.
He was elected to Labour's policy council in 2012 and became a member of the New Zealand Labour Party Council in 2013.
The 63-year-old said standing for Labour President was a way to give back to his adopted country, where his children have grown up.
He heads the management and international business department at the University of Auckland and specialises in international labour movements.
"Politically I think you have to get over what I call the credibility hurdle - you have to be seen to be a government-in-waiting.
"Despite having good policies ... we never quite got over that initial credibility hurdle."
Professor Haworth, who has worked as a union president and sat on the Ports of Auckland board, replaces Moira Coatsworth, who stood down in December following Labour's election defeat.
He said Labour had been much too introverted and focused on its own constitutional and other matters in the three years running up to last year's election.
Fundraising also needed to be improved, he said.
Labour spent half as much as National on last year's election campaign and was outspent by the Greens for the first time.
"National has a very good fundraising apparatus. And it is of course in that sense the party of wealth.
"It has access in a way that the Labour Party traditionally in New Zealand finds difficult to match.
"But I think we can professionalise our fundraising."
Labour had excellent policies, Professor Haworth said, but they had not been communicated well to voters.
He rejected talk of any move to the political centre: "It is much more bringing people to you than you moving somehow to this notion of where they are."
He said Prime Minister John Key was a "extraordinary politician". But history showed governments were susceptible to "third-term blues".
Nigel Haworth
• New Labour president heads the management and international business department at the University of Auckland.
• The 63-year-old moved to New Zealand from Scotland in 1988.
• Wants Labour to be "relentlessly outward-looking".