Socceroos defender Brad Smith has completed a return to the scene of his most successful period, joining Seattle Sounders on a permanent deal.

The 26-year-old, released by English club Bournemouth in July following the Cherries' relegation from the Premier League, signed for the MLS club on Thursday.

It's a happy reunion for Smith, who was on loan at the Sounders from August 2018 to December 2019.

During his previous stint in America's Pacific northwest, Smith won his way back into the Socceroos squad after being overlooked for the 2018 World Cup and also helped the club win the 2019 MLS Cup.

"This place has a special place in my heart ever since I arrived here," the left-back said.

"Going away from it was quite upsetting. Being back (in England), it was difficult. I always knew that I wanted to come back."

Smith will be hoping for more success in Seattle after a largely underwhelming 12 years in England.

After coming through as a junior at Premier League giants Liverpool, Smith made just five appearances for the Reds before moving to Bournemouth.

Injuries hampered his time with the south coast club, making just five appearances in four seasons and spending most of his time on loan at Seattle and then English Championship club Cardiff.

"I feel like I can add what I brought last time and hopefully push for back-to-back MLS Cups," said Smith, who has 22 caps for the Socceroos.