Hahnemann rejoined MLS on Friday, landing back in his hometown of Seattle after the Sounders traded for the top allocation spot.
"This is where I started my career and I wanted to finish here," said Hahnemann. "This is what we've always dreamed would happen in Seattle, and what I always wanted when I was here."
After winning the A-League in 1996, Hahnemann joined the Colorado Rapids. Three years there preempted a move to the English Premier League, initially with Fulham. The now-40-year-old has played over 300 times in England for Fulham, Reading, Wolverhampton and Everton.
He's also been on the roster to two World Cups and has nine international caps for the United States.
"Adding Marcus for the final stretch gives us experience and quality on and off the field to supplement our current core of goalkeepers," said Sounders FC head coach Sigi Schmid.
Seattle had to dish a conditional draft pick to Toronto FC to move to the top of the allocation rankings. The team already employs goalkeepers Michael Gspurning, Bryan Meredith, Andrew Weber and Josh Ford.
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