Weber, 28, has trained with the Sounders throughout the 2012 preseason.
The goalkeeper made two MLS starts in three seasons with San Jose before joining Seattle.
Weber began his professional career with DC United in 2005 but got most of his experience with the Montreal Impact of the USL First Division where he made 29 regular season appearances for the club.
"Andrew adds a goalkeeper who has had Champions League experience with Montreal and who has been in MLS for the last few years," said Sounders FC head coach Sigi Schmid. "Obviously our goalkeeping situation has changed dramatically from last year with Kasey Keller retiring and Terry Boss having to retire. We are happy with our goalkeepers, and adding Andrew Weber gives another capable keeper."
On a similar note, the Philadelphia Union signed goalkeeper Chris Konopka, a former Kansas City draftee.
Konopka, 26, was most recently a member of the MLS Goalkeeper Pool. He has also spent time with the New York Red Bulls and Columbus Crew. Per club and league policy, terms of the deal were not disclosed.
The Toms River, NJ native will likely battle for playing time as Zac MacMath's backup during the 2012 MLS Season.Follow GOAL.COM USA on