White was drafted by the Swift Current Broncos of the Western Hockey League in the 5th round, 89th overall in the 1999 WHL Bantam Draft. His first season with Swift Current was fairly successful, as he scored 12 goals and 31 assists in 69 games, which placed him seventh on the team in scoring. They finished the season first in the division. In White's second season with Swift Current, he fared much better, scoring 32 goals, 47 assists and 79 points in 70 games, which placed him in second place on the team in scoring. This gave NHL teams interest in drafting him.
White was drafted in the 2002 NHL Entry Draft by the Toronto Maple Leafs. The Leafs picked White in the 6th round, 191st overall. In 2002–2003, White finished third on Swift Current in scoring, with 24 goals, 44 assists and 68 points in 64 games, and was named to the WHL's First All Star Team and the CHL's Second All Star Team. White played for Team Canada at the 2003 World Junior Championship in Halifax, where Canada finished second place to Team Russia. White was primarily the seventh defenceman and powerplay specialist for Canada, where he scored 2 goals and 4 assists for 6 points in 6 games, and was one of the surprises of the tournament. White broke his left ankle in late October 2004 and thereby could not be offered a spot on the 2004 World Junior Team.
In the 2005–2006 season, White was named to Team Canada for the Spengler Cup as one of 8 defenceman on the club. Canada made it into the final against Metallurg Magnitogorsk, losing by a score of 8–3. White accumulated 1 goal in the tournament. He also made his debut with the Maple Leafs, and scored five points (one goal and four assists) in his first five career NHL games.
In 76 games for the Maple Leafs in the 2006–2007 season, he scored 3 goals and had 23 assists for a total of 26 points, leaving him tied for second in scoring among rookie defencemen. White spent much of the season playing with Hal Gill, giving rise to the nickname of "Barney and Fred", referencing the famous Flinstones characters. The nickname was given due to the almost full foot in height Gill has on White, as well as the massive weight difference.
White has recently begun to play in the right wing position, as opposed to his natural defence. In the 2008-09 season, White began the season as a healthy scratch, until injury troubles for the Leafs forced the team to activate White and place him in a forward line. White responded well initially, scoring a goal in his first game of the season and scoring 7 points in the first 15 games. He has since returned to the defence position due to further injuries to the Maple Leafs defensive core.