At provincial level, he played mainly with Auckland, though he spent one season with Tasman and was also loaned out to Nottingham in England's second-level RFU Championship in 2010.

The following year he was named in the Blues squad for the Super 12 and made his debut against the Hurricanes in the opening game of the season, on 22 February 2002.

In 2007, Williams was one of the 22 players withdrawn from the first half of the Super 14 season to attend a "conditioning camp", as part of the All Blacks' World Cup preparations.

A few weeks later, "for disciplinary reasons", Williams was left out of the squad to face the Sharks in Durban in a S14 semi-final match – which the Blues lost – and returned home to Auckland.

He started in all three matches against touring Northern Hemisphere teams, in June 2003, though he could have missed the games against Wales and France, after being cited for stamping on the head of England fullback Josh Lewsey;[17] he was cleared of the charge when a disciplinary tribunal ruled that his actions had been "inadvertent and incidental".

He almost did not make the squad, after suffering a stress fracture of the right foot during the All Blacks training camp in New Plymouth, an injury that required the insertion of a pin, but was included on the strength of his line-out play.

[19] He was rested for the first two pool matches, against Italy and Canada, but started in the remaining five games that New Zealand played, scoring his first international try in the final pool game, against Wales, when he jumped above the Welsh wing Shane Williams, to collect a cross-field kick from Carlos Spencer.

[20][21] French back, and newspaper columnist, Thomas Castaignède named Williams and England's winning captain, Martin Johnson as the locks in his "team of the tournament".

[29] After an indifferent performance against Australia – according to coach Graham Henry, "we thought Ali Williams had an opportunity on Saturday and didn't take it"[30] – Williams was dropped from the squad for New Zealand's last game in the 2004 Tri Nations, against South Africa, who won comprehensively, out-scoring the All Blacks by five tries to two.

Despite a lack of game time during the 2005 Super 12 season – he was suspended for six weeks after being found guilty of trampling on fellow All Black Richie McCaw during the game between the Blues and Crusaders[31] – Williams was chosen to start in the opening Test of the All Blacks season, a 91–0 rout of Fiji,[32] during which he scored his second international try.

It was during this time in which he spoke of an incident involving Clint Brown then TV anchor for 3 News who was stripped naked by Williams and members of the All Black team and had his eyebrows shaved off after becoming heavily intoxicated on a flight from South Africa to Australia.

Williams was selected in the squad to face Ireland,[39] but suffered a syndesmosis injury – commonly referred to as a high ankle strain – during a training session.

[42] Williams was named on the bench for the first match in the 2006 Tri Nations Series, against Australia in Christchurch; he replaced Jason Eaton with 20 minutes remaining and came close to creating a try when he leapt high to retrieve a cross-field kick from Dan Carter, tapping it back to wing Rico Gear, who was unable to hold on to the ball.

Williams again came off the bench with less than an hour gone, and then played the full 80 minutes in the All Blacks' remaining two fixtures, both against South Africa away from home.

[45] Williams's troubles with the Blues had no impact on his international career, as he was included in the New Zealand squad for the two-Test series against France in June 2007.

But despite having his jaw wired and being forced to subsist on soup for several weeks,[46] he made a return to rugby for his club side, Ponsonby, at the end of July, scoring two tries, and started for Auckland in their Air New Zealand Cup match against Bay of Plenty on 3 August, scoring a try in the fourth minute of the game.

Following his return from injury, Williams was an automatic selection for the 2007 Rugby World Cup, especially as two other locks, James Ryan and Jason Eaton were unavailable owing to long-term injuries and Keith Robinson had suffered a calf strain during the Tri Nations and was a doubtful starter, at least for the first pool game.

Robinson suffered a recurrence of his calf strain during pre-tournament training, which left Williams and Chris Jack to share the locking duties during the early games.

[52][53] His younger brother, Jay, is also a rugby footballer, who played at lock for Auckland and has several caps for London social club Kew Occasionals.

Together with former Blues and All Blacks teammate Doug Howlett, Williams is an official patron of the KidsCan Charitable Trust, a national charity dedicated to the welfare of financially disadvantaged New Zealand children.