During Keith's second college season, he left the Spartans after 15 games to join the major junior ranks.He returned to British Columbia to play for the Kelowna Rockets of the Western Hockey League (WHL) and amassed 46 points (11 goals and 35 assists) over 37 regular season games with a 32 plus-minus in his single season there. Keith was selected by the Chicago Blackhawks in the second round, 54th overall, of the 2002 NHL Entry Draft.After splitting the next year between Michigan State and the Kelowna Rockets of the Western Hockey League (WHL), he spent two seasons with the Norfolk Admirals of the American Hockey League (AHL).In 2005–06, he played his NHL rookie season with the Blackhawks.He scored a goal in his Spartans debut in the Cold War, an outdoor game at Spartan Stadium against the state-rival University of Michigan Wolverines on October 6, 2001, that set a record for attendance at a hockey game.He completed his freshman year with three goals and 15 points in 41 games, ranked fourth among team defencemen behind John-Michael Liles, Brad Fast and Andrew Hutchinson.
He recorded seven goals and 25 points over 75 games in his professional rookie season in 2003–04.
He made an immediate impact on the club, scoring nine goals and 21 points, while averaging over 23 minutes of ice time in 81 games during his 2005–06 NHL rookie season.
The Blackhawks re-signed him in the off-season to a four-year contract extension.
He was rewarded for this effort by a selection to his first NHL All-Star Game in 2008.
Keith went on to finish the season with 12 goals and 32 points, along with a 30 plus-minus rating, despite being on a non-playoff team.