The 41-year-old former Crown prosecutor has held a raft of senior portfolios, including energy, labour, transport and economic development and communications.
"All of that gives me the experience, the acumen, and the drive to do this job very well," he said yesterday.
While he was unsuccessful in his bid to be deputy leader last year, he has proven to be a strong voice in the Opposition benches, launching a series of telling attacks on the new Government.
His decisions to date show he is willing to play the long game - and has the ability to match it with popular Labour leader Jacinda Adern.
He says other MPs had encouraged him to put his name forward, and though he could not say whether he has the numbers to win, he has "strong support".
He will face strong competition in the race for the leadership but it's fair to say he has made a very decisive start.