The veteran midfielder is heading to Seattle to reunite with Sigi Schmid, who coached him in Columbus.
Seattle acquired veteran midfielder Adam Moffat from the Houston Dynamo in exchange for midfielder Servando Carrasco and a 2014 second-round pick. The move came 90 minutes before the MLS roster freeze at 5 p.m. ET.
Moffat, 27, has been a stalwart in holding midfield for Houston this season, compiling a career-high 26 appearances (24 starts) while chipping in three goals. The Scotland native, who played under current Sounders coach Sigi Schmid from 2007 to 2008 in Columbus, has started each of the past two MLS Cups for Houston.
"He was a member our MLS championship team in Columbus and brings a fantastic attitude, has experience running the midfield, and a great shot from distance," Schmid said in a press release. "Although it is difficult to see Servando leave, I am excited to welcome Adam to our team."
The 25-year-old Carrasco has logged a career-high 19 matches (13 starts) himself in 2013, scoring one goal.
The Sounders, who signed USA captain Clint Dempsey last month, have won four straight and with a 14-8-4 record now lead MLS in points per game. Houston is 0-3-1 in its past four and at 10-10-7 finds itself in a tie for the final Eastern Conference playoff slot.