Harrington was manager Peter Vermes' first draft selection in 2007, when he was selected third overall from North Carolina. He was named the team's Rookie of the Year with three goals and four assists in 27 starts as a midfielder.
This past season, Harrington played in 11 matches, including nine starts, for Sporting, which finished with the best record in the Eastern Conference at 18-7-9 (63 points). KC reached the conference semifinals before being knocked out by the Houston Dynamo by a 2-1 aggregate score
For Portland, Harrington brings experience and adds another piece to a team that struggled in 2012. The Timbers finished second-to-last in the Western Conference with an 8-16-10 record (34 points), including an MLS-worst 1-12-4 mark on the road.
In his six seasons, Harrington has five goals and 14 assists and is tied for ninth all-time in games started for KC with 128.