The 34-year-old Austria international was a free agent after departing Madrid and has signed for Udinese until the end of the season.
Alaba arrives with an impressive CV, having won the Champions League four times during his career. He lifted the trophy twice with Bayern Munich and twice with Real Madrid.
However, he is joining an Udinese side that has collected just four points from their opening five Serie A matches after finishing 10th last season.
Alaba insists he has not moved to Italy simply to see out the final years of his career.
"I've had so many experiences and won so much throughout my career, but one thing hasn't changed - I want to win again," Alaba said after completing the move.
"I want to compete again. And I want to achieve something special once more. That is the mindset I'm bringing to Udinese."
The defender has not played since captaining Austria at the World Cup, where they were eliminated by eventual champions Spain in the last 32.
Alaba has won 117 caps for Austria and scored 15 goals for his country.
His arrival gives Udinese a player with vast experience at the top of European football, while the club will hope he can help strengthen their defence and push them up the Serie A table.
"I certainly haven't come to wind down my career," Alaba added.
"I'm still too ambitious for that, and I still strongly believe in what I can do on the pitch.
"I want to keep pushing, perform at the highest level in Serie A week in and week out, and achieve something meaningful.
"I'm really excited about this challenge, and I still have a lot to prove to myself."
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