He captained New Zealand at the 2019 Cricket World Cup, leading the team to the final and winning the Player of the Tournament award in the process.

Ian Chappell and Martin Crowe have ranked Williamson among the top four or five Test cricket batsmen, along with Joe Root, Steve Smith, Virat Kohli of the current era.

[9] The late former New Zealand cricketer, Martin Crowe, noted that, "we're seeing the dawn of probably our greatest ever batsman" in Williamson.

All three were accomplished volleyball players, and Anna and Sophie were in New Zealand age group teams.

[16] Williamson made his debut for Northern Districts in 2007 at the age of 17, who he has remained with for the duration of his New Zealand domestic career.

[17][18] He scored his first T20 hundred, on 19 September 2014, making 101* in 49 balls to guide Northern Districts to a comfortable win against Cape Cobras in Champions League Twenty20 2014.

In February 2015, a Williamson signed for Indian Premier League side Sunrisers Hyderabad (SRH).

[26][27] Under Williamson's captaincy, Sunrisers Hyderabad finished runners-up and he was the season's leading scorer with 735 runs.

[32] In the 2021 The Hundred season, Williamson was drafted for Birmingham Phoenix but withdrew because of an ongoing elbow injury.

He scored his maiden ODI century against Bangladesh on 14 October 2010 in Dhaka and hence became the youngest centurion in New Zealand's cricket history.

[39] He was also named as captain ahead of the ODI and Twenty20 series against Pakistan in December 2014 as McCullum was rested.

[40] Williamson scored 100* off 69 balls against Zimbabwe at Bulawayo, which at the time was the second fastest century by a New Zealander in a One-Day International.

[41] He also established one of the most potent top-order partnership with Ross Taylor, with Williamson himself being the most prolific number-three batsman for the national side since former captain Stephen Fleming.

On 15 November 2015 Williamson and Taylor became the first pair of away batsmen to each score 2nd innings centuries at WACA Ground in Perth.

[45] In March 2016, Williamson assumed the position of captain of New Zealand across all forms of cricket after the retirement of Brendon McCullum, beginning with the World T20I cup in India.

He completed this in the fewest innings,[needs update] the quickest time from his Test debut and became the youngest player to achieve this feat.

[51] Later that year, he scored his 10,000th run in first-class cricket, batting for the English side Yorkshire in the 2018 County Championship.

On 7 December 2018, Williamson became the first player from New Zealand to cross 900 rating points in the ICC Test batting rankings.

[69][70] In June 2021, he led New Zealand to victory in the inaugural ICC World Test Championship, beating India in the final by eight wickets.

In August 2021, Williamson was named as the captain of New Zealand's squad for the 2021 ICC Men's T20 World Cup.

[71] Under his captaincy, New Zealand reached their third consecutive ICC event final across all formats after beating England in the semi-final of the T20 World Cup.

[72] In the final, Williamson scored a brilliant knock of 85 off 48 balls but ended up on the losing side after facing defeat to Australia by 8 wickets.