The All Blacks Assistant Coach and forwards coach first followed Graham Henry to Wales as his assistant before taking over the top job himself when Graham returned to New Zealand in 2002.
He led Wales to a quarterfinal berth at the 2003 Rugby World Cup, a campaign which was highlighted by the almighty scare the Welsh side gave the All Blacks in their pool match when the Welsh were leading with 20 minutes to play.
In 2004, he was appointed to the All Blacks as an assistant coach under former mentor Graham Henry. Hansen was considered as a likely candidate to become the next Crusaders coach, starting in the 2009 Super 14 season, after Robbie Deans left to coach Australia, but in fact the Crusaders coaching job went to former All Black Todd Blackadder
Steve assisted Graham Henry in coaching the All Blacks to a 2011 Rugby World Cup final win against France, ending a 24-year Rugby World Cup winning drought for the All Blacks. It was tipped that Steve Hansen would take over as head coach of the New Zealand All Blacks when Graham Henry's contract expired at the end of 2011. He was formally appointed on 15 December 2011.
In his first games and series as head coach he guided the All Blacks to a 3–0 series victory over the Irish during 2012 tour, with the final game being a record 60–0 defeat for the Irish. On 25 August, the All Blacks under Hansen retained the Bledisloe Cup for a 10th consecutive year after their second match against Australia during the 2012 Rugby Championship. He was named IRB Coach of the Year for 2012. His only defeat as coach in 2012 came against England, a 38–21 loss on 1 December 2012 in the 2012 end-of-year rugby union tests.
In the 2012 Queen's Birthday and Diamond Jubilee Honours Hansen was appointed a Companion of the New Zealand Order of Merit, for services to rugby.
The All Blacks went undefeated in 2013, and Hansen was named IRB coach of the year for the second year running. The All Blacks retained the Rugby Championship and Bledisloe Cup, and won 14 of 14 matches, becoming the first team to ever do this in the professional era. The team finished the year by winning 24–22 against Ireland in the 2013 end-of-year rugby union tests.
In 2014, having already defeated England 3–0 on their tour, New Zealand lost their first ever Rugby Championship match. On 4 October, they lost to South Africa 27–25 in Johannesburg, while they had also drawn their opening match of the Championship with Australia 12–all. Despite this, they retained their title for a third consecutive year. On 1 November 2014, Hansen led the All Blacks to a 74–6 win over the United States in Chicago - this was the first time the All Blacks had visited the States in the professional era, and the first time the USA had hosted them since 1980. Hansen later led the team to a further three victories on their European tour, to see him be named World Rugby coach of the year.
In 2015 Hansen took the All Blacks to Samoa for the first ever official test match, where the All Blacks won the match 25–16. To cap a week he described as perfect, All Blacks coach Steve Hansen has received an honorary chief title at a moving ceremony in Apia.
In a shortened Rugby Championship, the All Blacks failed to retain the title they held for three years. Having beaten Argentina 39–18 and South Africa 27–20, a final match against Australia would see either New Zealand or Australia claim the Championship. For the first time since 2011, Australia beat the All Blacks 27–19. During the 2015 Rugby World Cup, despite some error ridden games in the Pool stage, Hansen lead the All Blacks to the top off Pool C with victories over Argentina, 26–16, Namibia 58–14, Georgia 43–10 and Tonga 47–9, before beating France in the quarter-final 62–13 and South Africa 20–18 in the semi-final.
They faced Australia in the final, winning 34–17 to become the first team ever to retain the Webb Ellis Cup. He also led the All Blacks to their first ever foreign Rugby World Cup victory. They also became the second team to win on British soil with Australia having won both previous tournaments in 1991 and 1999.